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A2 level Biology notes

Unit 4- Populations and the Environment

1. Populations 3 1.1 Populations and ecosystems 3 1.2 Investing populations 3 1.3 Variation in population size 5 1.4 Competition 6 1.5 Predation 8 1.6 Human populations 10
2. ATP 12 2.1 Energy and ATP 12
3. Photosynthesis 14 3.1 Overview of Photosynthesis 14 3.2 The Light- dependent reaction 16 3.3 The Light Independent Reaction 17 3.4 Factors Affecting Photosynthesis 18
4. Respiration 20 4.1 Glycolysis 20 4.2 Link reaction and Krebs cycle 21 4.3 The electron transport chain 23 4.4 Anaerobic respiration 24
5. Energy and Ecosystems 25 5.1 Food chains and Food webs 25 5.2 Energy Transfer between Trophic Levels 26 5.3 Ecological Pyramids 27 5.4 Agricultural Ecosystems 28 5.5 Chemical and Biological Control of Agricultural Pests 29 5.6 Intensive Rearing of Domestic Livestock 31
6. Nutrient Cycles 33 6.1 The carbon cycle 33 6.2 The greenhouse effect and global warming 34 6.3 The Nitrogen Cycle 35 6.4 Use of Natural and Artificial Fertilisers 36 6.5 Environmental consequences of using nitrogen fertilisers 36
7. Ecological Succession 37 Succession 37 7.2 Conservation of Habitats 38
8. Inheritance and Selection 39 8.1 Studying inheritance 39 8.2 Monohybrid Inheritance 40 8.3 Sex Inheritance and Sex Linkage 41 8.4 Co-dominance and Multiple Alleles 42 8.5 Allelic Frequency and Population Genetics 43 8.6 Selection 44 8.7 Speciation 45

1. Populations
1.1 Populations and ecosystems

❖ Ecosystem- It is made up of all the interacting biotic and abiotic features in a specific area ❖ Population- A group of interbreeding organisms of one species in a habitat. ❖ Community- All the populations of different organisms living and interacting in a particular place at the same time. ❖ Habitat -The place where a community of organisms lives. ❖ Ecological niche- All the biotic and abiotic conditions required for an organism to survive, reproduce and maintain a viable population. No 2 species occupy exactly the same niche.

1.2 Investing populations

❖ To study habitat often necessary count no individuals of species in given space ❖ This known as abundance ❖ Virtually impossible identify & count every organism ❖ Do so would time consuming & cause damage habitat being studied ❖ SO small samples usually studied in detail ❖ As long as samples representative of habitats as whole any conclusion drawn from findings will be valid ❖ No sampling techniques used in study of habitat, these include: ➢ Random sampling using frame or point quadrats ➢ Systematic sampling along transects
Quadrats
❖ Three factors to consider when using quadrats: ❖ Size quadrat use: depend upon size plants or animals being counted & how they distributed within area. Large species = larger quadrat ➢ Where species occurs in series group rather being evenly distributed throughout area, a large no small quadrats will give more representative results than small no large ones ❖ No of sample quadrats to record within the study area: larger no of sample quadrats the more reliable results will be. ➢ Recording species w/in quadrat is time-consuming task, needs balance between validity results & time available. ➢ Greater no different species present in area studied = greater no quadrats required valid results ❖ Position each quadrat w/in study area: produce statistically significant results technique random sampling must used.
Random Sampling ❖ Important sampling random avoid any bias in collecting data, avoiding bias ensures data obtained valid ❖ A good method of random sampling is to: 1. Lay out two long tape measures @ right angles, along 2 sides of study area 2. Obtain series of coordinates by using random no taken from table or grated by computer or calculator 3. Place quadrat at intersection of each pair coordinates & record species w/in it

Systematic sampling along transects ❖ Sometimes more informative measure abundance & distribution of species in systematic rather random manner ❖ Particularly important where some form transition in communities plants & animals take place ❖ Line transect comprise string or tape stretched across ground in straight line, any organism over which line passes is recorded ❖ Belt transect is strip, usually meter wide, marked putting second line parallel to first, species occurring w/in belt between lines recorded
Measuring abundance ❖ Random sampling w/ quadrats & transects used obtain measures abundance ❖ Abundance no individuals of species w/in given space ❖ Can measured several ways, depending on size species being counted & the habitat, e.g.: ➢ Frequency: likelihood of particular species occurring in quadrat, e.g. a species occurs 15/30 quadrats frequency is 50%. Method useful where species is hard count, gives quick idea species present & general distribution. Does not provide info on density & detailed distribution species ➢ Percentage cover: an estimate area w/in quadrat that particular plant species covers. Useful where species is particularly abundant or diff count. Advantage is data collected rapidly & individual plants not need counted, less useful where organisms occur several overlapping layers. ❖ Obtain results, necessary ensure sample size is large, many quadrats used & mean all samples obtained. Larger the no samples, more representative community as whole will be results

1.3 Variation in population size

❖ A population is group interbreeding individuals of same species in a habitat ❖ Number individuals in population is population size ❖ All populations are different organisms that live & interact together are known as a community
Population Growth Curves ❖ Usual pattern of growth for natural population has 3 phases:
1. Period of slow growth as the initially small number of individuals reproduce to slowly build up their number
2. Period of rapid growth where the ever-increasing number of individuals continue to reproduce. The population size doubles during each interval of time
3. Period when population growth declines until its size remains more or less stable. The decline may be due to food supply limiting numbers or to increase population. Graph therefore levels out with only cyclic fluctuations due to variations in factors such as food supply or the population size of predators
Population Size ❖ Imagine situation in which single algal cell, capable asexual reproduction, placed newly created pond ❖ Summer & so plenty light & temp water around 12oC, mineral nutrients been added to water ❖ These circumstances algal cell divides rapidly as all factors needed for growth population present ❖ Are no limiting factors ❖ In time, things change: 1. Mineral ions used up as population becomes larger 2. Population becomes so large that the algae at surface prevent light reaching those at deeper levels 3. Other species introduced into pond, carried by animals or wind, and some these species may use algae as food or compete for light or minerals 4. Winter brings lower temp & light intensity of shorter duration ❖ As result population slows and may possibly diminish, ultimately population likely reach relatively constant size ❖ There many factors (both biotic & abiotic) will affect the ultimate size ❖ Changes these factors will influence rate growth & final size population ❖ SUMMARY: no population continues grow indefinitely as certain factors limit growth, e.g. availability food, light, water, oxygen & shelter & accumulation toxic waste, disease & predators ❖ Each population has max size can be sustained over relatively long period, this is determined limiting factors ❖ Various limiting factors affect size population are of 2 types: 1. Abiotic Factors: non-living part 2. Biotic factors: activities living organisms
Abiotic Factors
Abiotic features that influence size population include: ❖ Temperature: each species has different optimum temp at which best survive. Further away from optimum small population be supported. In plants enzymes work more slowly & metabolic rate reduced. Populations grow more slowly. Temp above optimum, enzymes work less efficiently as gradually undergo deterioration. AGAIN population grows more slowly Warm-blooded animals, birds & mammals, maintain relatively constant body temp regardless external temp. Might think population growth & size unaffected temp. BUT further temp external environment gets from their optimum more energy expend to maintain normal temp. Leaving less energy individual growth & so mature more slowly & reproductive rate slows. Population size therefore smaller ❖ Light: as ultimate source energy for ecosystems, light basic necessity life. Rate photosynthesis increases as light intensity increases. Greater rate photosynthesis, the faster plants grow & more spores/seed produced. Their population growth & size therefore potentially greater. In turn population animals that feed on plants potentially larger ❖ pH: this affects action enzymes. Each enzyme has optimum pH at which operates most effectively. Population of organisms is larger where appropriate pH exists & smaller, or non-existent where pH very different from optimum ❖ Water & Humidity: where water is scarce, populations are small & consistent only of species that are well adapted living in dry conditions. Humidity affects transpiration rates in plants & evaporation water from bodies of animals. Again, in dry air conditions, populations species adapted to tolerate low humidity will be larger than those with no such adaption.

1.4 Competition

❖ When 2 or more individuals share any resources (e.g. light, food, space, oxygen) that is insufficient satisfy all requirements fully = COMPETITION ❖ Where competition arises between same species: intraspecific competition ❖ Where competition arises between different species: interspecific competition
Intraspecific Competition ❖ Intraspecific competition occurs when individuals same species compete w/ one and other for resources ❖ It is availability of resources that determines size population ❖ Greater availability, larger the population, lower the availability smaller the population ❖ Examples ➢ Limpets competing for algae, main food. More algae available, larger limpet population becomes ➢ Oak trees competing resources, in large population small oak trees some grow larger & restrict availability light, water & minerals to rest which die. In time population be reduced relatively few large dominant oaks ➢ Robins competing breeding territory. Female birds normally only attracted males w/ breeding territories, each territory provides adequate food for 1 family. When food scarce territories have become larger provide enough food. Therefore fewer territories given area = fewer breeding pairs = smaller population
Interspecific Competition ❖ Occurs when individuals of different species compete for resources ❖ Where populations 2 species initially occupy same niece, 1 normally have competitive advantage ➢ Population this species gradually increase size while population other will diminish ➢ Conditions remain same, will lead complete removal one species ➢ Known as competitive exclusion principle – where 2 species competing limited resources, one uses resources most effectively ultimately eliminate other ❖ No two species can occupy same niece indefinitely when resources limiting ➢ Cormorant & Shags (sea birds) appear occupy same niece – living & nesting same type cliff face & eating fish from sea ➢ Analysis food shows shags feed largely on sand eels & herring, cormorants eat mostly flat fish, gobies & shrimps ➢ Therefore occupy different niches ❖ Show how factor influences size of population necessary like birth rate & death rate of individuals to population ❖ E.g. increase food supply not necessarily mean more individuals; just result bigger individuals ❖ Therefore important show how factor, such as change in food supply, affects number individuals in population ➢ E.g. decrease food supply lead individuals dying starvation, resulting in reduction population ➢ Increase food supply means more likely individuals survive & so increased probability will produce offspring & population will increase ▪ Effect therefore takes longer influence population

Application – Effects Interspecific competition ❖ Many cases we suspect competition is reason variations in population. Practice difficult prove for number reasons: ➢ Many other factors influence population size, such as abiotic factors ➢ Casual like be established show that competition is cause of observed correlation ➢ Time lag in many cases competition & so population change may due competition took place years earlier ➢ Data natural population sizes hard to obtain & not always reliable
HINT
Although population of 1 species may increase as another decrease, this does not prove that this is due to direct competition between them. To be certain, it is necessary to establish a casual like for the observed correlation

1.5 Predation

Predation occurs when one organism is consumed by another.
Effect of predator-prey relationship on population size ❖ Predators eat their prey, thereby reducing the population of prey. ❖ With fewer prey available the predators are in greater competition with each other for the prey that are left. ❖ The predator population is reduced as some individuals are unable to obtain enough prey for their survival. ❖ With fewer predators left, less prey is eaten. ❖ The prey population therefore increases ❖ With more prey now available as food, the predator population in turn increases. [pic]

1.6 Human populations

Human population size and growth rate
Most of our history has been kept in check by food availability, disease, predators and climate. Two recent events have lead to an explosion in human population: ❖ The development of agriculture ❖ The development of manufacturing and trade that created the industrial revolution.
Factors affecting the growth and size of human populations
The basic factors that affect the growth rate of human populations are birth rate and death rate.
Individual populations are further affected by migration, which occurs when individuals move from one population to another. There are two types: ❖ Immigration, where individuals join a population from outside. ❖ Emigration, where individuals leave a population.
Population growth = (births + immigration) - (deaths + emigration)
Factors effecting birth rate
Economic conditions - countries with a low per capita income tend to have higher birth rates.
Cultural and religious backgrounds - some countries encourage larger families and some religions are opposed to birth control.
Social pressures and conditions - in some countries a large family improves social standing.
Birth control - the extent to which contraception and abortion are used markedly influences the birth rate
Political factors - governments influence birth rates through education and taxation policies.
Birth rate = number of births per year x100 total population in the same year
Factors effecting death rate
Age profile - the greater the proportion of elderly people in a population, the higher the death rate is likely to be. ❖ Life expectancy at birth - the residents of economically developed countries live longer than those of economically less developed countries. ❖ Food supply - an adequate and balanced diet reduces death rate ❖ Safe drinking water and effective sanitation - reduce death rate by reducing the risk of contracting water-borne diseases such as cholera. ❖ Medical care - access to healthcare and education reduces the death rate. ❖ Natural disasters - the more prone a region is to a drought, famine of disease the higher its death. ❖ War - deaths during wars produce an immediate drop in population and a longer term fall as a result of fewer fertile adults. ❖ Death rate = number of deaths per year x100 total population in the same year
Population structure
Age population pyramid
There are three typical types of population pyramids: ❖ Stable population - where the birth rate and the death rate are in balance and so there is noincrease of decrease in the population size. ❖ Increasing population - where there is a high birth rate, giving a wider base to the population pyramid (compared to a stable population) and fewer older people, giving a narrower apex to the pyramid. This type of population is typical of economically less developed countries. ❖ Decreasing population - where there is a lower birth rate (narrower base of the population pyramid) and a lower mortality rate leading to more elderly people (wider apex to pyramid). This type of population occurs in certain economically more developed countries, such as Japan.
Survival rates and life expectancy
A survival curve plots the number of people alive as a function of time. Typically it plots the percentage of a population still alive at different ages but it can also be used to plot the percentage of a population still alive following a particular event, such as a medical operation or the onset of a disease.
The average life expectancy is the age at which 50 per cent of the individuals in a particular population are still alive. It follows that life expectancy can be calculated from a survival.

2. ATP
2.1 Energy and ATP ❖ In most ecosystems the initial source of energy is the sun (light energy) ❖ Plants use solar energy for photosynthesis to make organic molecules, this takes place inside the chlorophyll inside chloroplasts which are mainly found in the spongy mesophyll of a leaf

❖ Carbon dioxide is taken in through the stomata ❖ Water is taken in through the roots ❖ Light is absorbed by the green pigment chlorophyll ❖ Oxygen is released into the atmosphere through the stomata ❖ Glucose is transported in solution for use or is stored as starch ❖ Energy is defined as the ability to do work ❖ Takes a variety of different forms- light, heat, sound, electrical, magnetic, mechanical, chemical and atomic ❖ Can only be changed form one form to another, cannot be created or destroyed ❖ Measure in joules (J) ❖ Organisms need energy for ➢ Metabolism- reactions within living organisms ➢ Movement e.g. circulation of blood and locomotion ➢ Active transport- the net movement of particles against a concentration gradient across a plasma membrane ➢ Maintenance, repair and division of cells and organelles ➢ Production of substances e.g. enzymes and hormones ➢ Maintenance of body temperature in birds and mammals (endothermic organisms) ❖ The flow of energy through living organisms occurs in 3 stages: Light energy from the sun is converted by plants into chemical energy during photosynthesis, the chemical energy in the form of organic molecules is converted into ATP during respiration in all cells, this is then used to perform useful work ❖ Adenosine triphosphate has 3 phosphate groups, a 5 carbon ribose and an adenine group

❖ The bonds between the phosphate groups are unstable and have a low activation energy so they are easily broken, when they are they release energy, it is the terminal phosphate that is removed. ❖ This is known as a hydrolysis reaction ❖ The reaction can also be reversed to made ATP from ADP through a condensation reaction ❖ The synthesis of ATP from ADP occurs in 3 different ways 1. Photophosphorylation- takes place in the chlorophyll containing plant cells during photosynthesis 2. Oxidative phosphorilation- occurs in the mitochondria of a plant and animal cells during the process of electron transport 3. Substrate level phosphorilation- occurs in plant and animal cells when phosphate groups are transferred from donor molecules to ADP to make ATP ❖ not a good store of energy due to unstable bonds, but good as an immediate source of energy for same reason ❖ Each ATP molecule releases less energy than each glucose molecule therefore released in smaller more manageable amounts ❖ The hydrolysis of ATP to ADP is a single reaction that releases immediate energy whereas the breakdown of glucose is a long series of reactions ❖ ATP is the source of energy for: 1) Metabolic processes polysaccharide synthesis from monosaccharide, polypeptide synthesis from amino acids and DNA/RNA synthesis from nucleotides 2) Movement- muscle contraction 3) Active transport- ATP provides energy to change the shape of the carrier proteins, allows molecules or ions to be moved against a concentration gradient 4) Secretion- needed to form the lysosomes 5) Activation of molecules- lowers the activation energy of molecules so they are more reactive so enzyme catalysed reactions can occur more readily

3. Photosynthesis
3.1 Overview of Photosynthesis

Site of photosynthesis - the leaf
Structure of the leaf is adapted to bring together the three raw materials of photosynthesis. (Water, carbon dioxide and light) and remove its products (oxygen and glucose). These adaptations include. ❖ A large surface area that collects as much sunlight as possible. ❖ An arrangement of leaves on the plat that minimises overlapping and so avoids the shadowing of one leaf by another. ❖ Thin, as most light is absorbed in the first few millimetres of the leaf and the diffusion distance is thus kept short. ❖ A transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells beneath. ❖ Long narrow, upper mesophyll cells packed with chloroplasts that collect sunlight. ❖ Numerous stomata for gaseous exchange ❖ Stomata that open and close in response to changes in light intensity ❖ Many air spaces in the lower mesophyll layer to allow diffusion of CO2 and oxygen. ❖ A network of xylem that brings water to the leaf cells and phloem that carries away the sugars produced in photosynthesis
Outline of photosynthesis

❖ Capturing of light energy - by chloroplast pigments such as chlorophyll ❖ The light dependent reaction- in which light energy is converted into chemical energy. During the process an electron flow is created by the effect of light on chlorophyll and this causes water to split (photolysis) into protons, electrons and oxygen. The products are reduced NADP, ATP and oxygen. ❖ The light-independent reaction - in which these protons (hydrogen ions) are used to reduce carbon dioxide to produce sugars and other organic molecules. Structure and role of Chloroplasts in photosynthesis ❖ Photosynthesis takes place inside the chloroplasts ❖ They are surrounded by a double membrane ❖ Inside the chloroplast membrane there are 2 distinct regions: - The grana- stacks of thylokoids where the light-dependent reaction takes place, contains the chlorophyll and can have tubular like structures to join them together called inter-granal lamellae - The stroma- fluid filled matrix where the light independent stage takes place, contain starch grains

3.2 The Light- dependent reaction

❖ Requires light ❖ Requires water ❖ Requires photosynthetic pigments ❖ Occurs in the thylokoids ❖ Light strikes chlorophyll and electrons are excited to a higher energy level where they are accepted by an electron carrier ❖ Photolysis occurs ❖ Electrons pass down the electron transfer chain to NADP firming ATP (Photophosphorylation- process by which ATP is made during the light reaction) ❖ Products are NADPH, ATP and O2 ❖ Oxygen produced comes from water ❖ NAPDH and ATP are then using in the Calvin cycle (light independent reaction)

3.3 The Light Independent Reaction ❖ Does not require light (can occur in both light and dark) ❖ Occurs in the stroma of the chloroplast

❖ Carbon dioxide from the atmosphere diffuses into the leaf through the stomata and dissolves in water around the walls of the mesophyll cells. It then diffuses into the plasma membrane, cytoplasm and chloroplast membranes into the stoma of the chloroplast ❖ In the stroma, the co2 combines with the 5-carbon RuBP using the enzyme RuBisCo ❖ Combination produces 2 molecules of glycerate 3-phosphate ❖ ATP and NADPH from light dependent reaction are used to reduce the activated glycerate 3-phosphate to triose phosphate ❖ The NADP is re-formed and goes back to light dependent reaction ❖ Some triose phosphate are converted to useful organic substrates such as glucose ❖ Most are used to regenerate RuBP using ATP from the light dependent reaction

3.4 Factors Affecting Photosynthesis Limiting Factors ❖ The law of limiting factors can be expressed as: At any given moment, the rate of a physiological process is limited by the factor that is at its least favourable value. ❖ Limiting factors of photosynthesis include light intensity, carbon dioxide concentration and temperature.
Light intensity ❖ No light - no photosynthesis. The light phase does not take place. ❖ Increasing the light intensity to value A causes photosynthesis to increase. The more light the greater the light phase and the greater the production of ATP to the Dark Phase. ❖ At light intensity A the rate of photosynthesis reaches its maximum and levels off. Some factor other than light intensity is limiting the rate of photosynthesis: it may be low temperature, low carbon dioxide, low chlorophyll content or the enzyme system is deficient (enzymes at maximum turnover number). ❖ Light intensity A is known as the 'saturation point' - the value beyond which light intensity is not a limiting factor. ❖ The rate of photosynthesis remains constant at maximum beyond light intensity A. The Increase in light intensity has no effect on the new limiting factor so photosynthesis stays the same.

Carbon dioxide concentration ❖ No carbon dioxide - no photosynthesis. ❖ Increasing the carbon dioxide concentration to value A causes photosynthesis to increase. The greater the supply of CO2, the faster the rate of enzyme activity ❖ At A the rate of photosynthesis reaches its maximum and levels off. Some factor other than CO2 is limiting the rate of photosynthesis: it may be low temperature, low light intensity ❖ The rate of photosynthesis remains constant at maximum beyond A. Increase in CO2 has no effect on the new limiting factor so photosynthesis stays the same.

Temperature ❖ At 0°C the rate of photosynthesis is low. Enzyme activity is low. Photosynthesis is an enzyme-controlled process. ❖ Increasing the temperature to 30°C increases the rate of photosynthesis. Enzyme activity increases. ❖ Maximum photosynthesis at 30°C. Enzyme activity at it maximum - maximum collision frequency between native enzymes and substrates. ❖ Photosynthesis declines beyond 30°C. Enzyme activity slowing due to denaturing of enzymes. ❖ No photosynthesis at 50°C. No enzyme activity - enzymes are denatured.

4. Respiration 4.1 Glycolysis

The splitting of the 6C glucose molecule into two 3C pyruvate molecules. ❖ Occurs in the cytoplasm of the cells. – Is an anaerobic process.

❖ Net production of 2 ATP molecules

❖ 2 molecules of pyruvate produces

❖ 2 molecules of reduced NAD produced (then used in the electron transport chain)

❖ Takes place in cytoplasm as glucose cannot enter the mitochondria due to size and enzymes used in the breakdown of glucose are found in the cytoplasm

4.2 Link reaction and Krebs cycle

The link reaction

❖ No energy is stored or removed in this reaction

❖ Occurs in the matrix of the mitochondria

❖ Pyruvate is converted into acytlycoenzyme A in this reaction

[pic]

❖ This occurs twice so... 2 molecules of Acytlycoenzyme A, 2 reduced NAD and 2 molecules of carbon dioxide are produced

The Krebs cycle

❖ Occurs in the matrix of the mitochondria

❖ Provides a continuous support of electrons to fuel the electron transport chain

❖ Produces a SMALL amount of ATP

❖ Occurs twice due to 2 acytylcoenzyme A molecules

❖ 6 molecules of NADH produced (reduced NAD)

❖ 2 molecules of FADH2 produced (reduced FAD)

❖ 2 molecules of ATP produced

❖ 4 molecules of carbon dioxide produced

❖ The NAD works with dehydrogenase enzymes that catalyse the removal of hydrogen ions and transfers then to other molecules such as hydrogen carriers involved in oxidative phosphorilation

4.3 The electron transport chain

❖ Energy from hydrogen atoms removed from compounds can be used to make ATP

❖ Energy carried by electrons, from reduced coenzymes (reduced FAD and NAD) is used to make ATP, involves electron transport chain and chemiosmosis.

❖ Occurs on the cristae of mitochondria. Hydrogen from glycolysis is used.

❖ Reduced NAD and FAD are oxidised, releasing Hydrogen atoms. The H atoms are split into H+ and e-.

❖ The regenerated NAD and FAD are reused in Krebs cycle.

❖ The electrons move along the electron transport chain (made up of 3 electron carriers), in a series of oxidation-reduction reactions, losing energy at each stage.

❖ Some of this energy is used to combine an inorganic phosphate with ADP to make ATP. The remaining energy is released as heat.

❖ The protons accumulate in the space between the 2 mitochondrial membranes before they diffuse back into the matrix of the mitochondria through protein channels.

❖ At the end of the chain, the electrons combine with these protons and oxygen to form H2O.

❖ Oxygen is the final acceptor of electrons in the electron transport chain.

❖ Without oxygen acting as the final acceptor of electrons, the H+ ions and electrons would ‘back up’ along the chain and respiration would come to a halt.

4.4 Anaerobic respiration

❖ Only Glycolysis can occur in the absence of oxygen

❖ There are 2 forms of anaerobic respiration: alcoholic fermentation in plants and lactate fermentation in animals

❖ The production of ethanol if exploited in the brewing process

❖ Pyruvate is converted to ethanal by decarboxillationn reduced NAD is then oxidised by the ethanal to give ethanol

❖ In animals, lactate is formed by the oxidation of reduced NAD by pyruvate

❖ The production of lactate regenerate the NAD and so Glycolysis can continue, a small amount of ATP is still produced to keep biological processes going

❖ An oxygen dept is created, lactate broken back down by oxygen at end

5. Energy and Ecosystems

5.1 Food chains and Food webs

➢ Organisms can be divided into 3 groups depending on how they obtain their energy

➢ Producers- Photosynthetic organisms that manufacture organic substances using light energy, water and co2 by photosynthesis

➢ Consumers- Obtain their energy by consuming other organisms. Primary consumers feed directly of plants (producers) these are then consumed by secondary consumers and then tertiary consumers (usually predators can be scavengers or parasites)

➢ Decomposers- feed off dead organic matter to obtain energy which is trapped inside them. Majority of them fungi and bacteria (decomposers) and to a lesser extent by animals such as earth worms (detritivors)

Food chains

➢ Describes a feeding relationship by showing the transfer of energy between producers and following consumers.

➢ Each stage is referred to as a trophic level

➢ Arrows represent the direction of energy flow

Food webs

➢ Most organisms in a community do not just feed upon one animal, and one animal can be fed upon by many other animals, a food web shows SOME of the feeding relationships within the community

➢ Not all of the relationships can be shown as it would be too complex

5.2 Energy Transfer between Trophic Levels

❖ Most energy is not converted by plants because, most of the suns light is reflected back into the atmosphere by clouds, not all wavelengths can be absorbed, light may not fall on the chlorophyll molecules and a limiting factor may stop the rate of photosynthesis e.g. low co2 levels

❖ The rate at which plants store energy is called net production:

Net production= gross production – respiratory loss

❖ Low % of energy transferred at each stage of the food chain is due to:

1. Some of the organism is not eaten

2. Some parts cannot be digested so lost in faeces

3. Lost in excretory materials (urine)

4. Lost as heat, maintaining body temperature

5. Movement during hunting etc

❖ Most food chains don’t have more then 4/5 trophic levels due to so much energy lost, insufficient energy to support more

❖ Total mass of organisms is less at higher trophic levels

❖ Total amount of energy stored is less at each trophic level

❖ Energy transfer (%) between each trophic level can be calculated by:

5.3 Ecological Pyramids

❖ Pyramids are drawn to show changes in number, biomass or energy

Pyramid of number

❖ Shows the number of organisms at each trophic level

❖ The more the wider the section of pyramid, the width of the block is proportional to the number of organisms present at each level

❖ Disadvantage: the range of numbers can be large

Pyramid of biomass

❖ The biomass of all living organisms at each trophic level can be calculated by:

Biomass = the number of individuals x mass of each individual

❖ Live mass can be used but gives unreliable results

❖ Not always practical/desirable to find the dry mass (mass of whales)

❖ Seasonal differences are not present and animal must be killed to get dry mass

❖ Units for biomass

Pyramid of energy

❖ Shows the flow of energy through each trophic level of an ecosystem during a fixed period of time

❖ Always a fixed pyramid shape

❖ Units for energy

5.4 Agricultural Ecosystems

❖ Made up of largely domesticated animals and plants used to produce food for mankind

❖ Tries to ensure that as much of the available energy from the sun is transferred to humans

❖ Increases the productivity of the human food chain

❖ Net productivity = gross productivity – respiratory loss

❖ Efficiency affected by the efficiency of the crop at photosynthesising and the area of the ground covered by the leaves of the crop

Comparison of natural and agricultural ecosystems:

|Natural Ecosystem |Agricultural Ecosystem |
|Solar energy only |Solar energy plus energy from food and fossil fuels |
|Lower productivity |Higher productivity |
|More species diversity |Less species diversity |
|More genetic diversity within a species |Less genetic diversity within a species |
|Nutrients are recycled naturally within an ecosystem |Natural recycling is more limited and supplemented by the |
| |addition of artificial fertilisers |
|Populations are controlled by natural means (competition, |Populations controlled by both natural and use of pesticides |
|climate) |and cultivation |
|Natural climax community |Artificial community prevented from reaching its climax |

Energy input

❖ To prevent an agricultural ecosystem from developing they remove all other species from a crop apart from the one they are growing

❖ To remove or suppress unwanted species requires an additional input of energy which comes in 2 forms, food for the farmers and fossil fuels for the machines.

Productivity

❖ Additional energy input increases productivity, controlling photosynthesis within a greenhouse would also do this as maximum photosynthesis can be achieved (CO2 levels controlled, temp controlled, water controlled, minerals controlled ect)

5.5 Chemical and Biological Control of Agricultural Pests

❖ A pest is an organism that competes with humans for food or space, pesticides are poisonous chemicals used to kill pests

❖ A pesticide should:

1. Be specific- harmless to humans and other organisms

2. Biodegrade- so it will break down into harmless substances in the soil but also needs to be chemically stable so has a long shell life

3. Be cost effective

4. Not accumulate- does not pass along food chain and harm other species higher up the food chain

Biological control

❖ Controlling a pest by using its natural predator or parasites of the pest

❖ Aim to control not eradicate- could be counterproductive, not enough pest for predator pest can increase in number again as predator dies

❖ Disadvantages:

1. Do not act as quickly, so could be time between introduction and significant control

2. Control may become a pest itself

|Biological Control |Chemical Pesticides |
|Very Specific |Always have some effect on other species |
|Once introduced, control organism reproduces itself |Must be reapplied – very expensive |
|Pests do not become resistant |Pests can develop genetic resistance – so new pesticides have|
| |to be developed |
|Risk that control organism becomes a pest – as pest population |Risk of accumulation in species or polluting nearby rivers |
|is reduced control feeds on crops | |

Integrated pest control systems

❖ Involves using all methods of pest control (chemical, biological and natural) to CONTROL the amount of pest

❖ Involves:

1. Choose a plant/animal that is immune as possible to the pest

2. Manage the environment to provide habitats suitable for predators

3. Monitor the crops for early signs of pests

4. Remove pests manually is exceeds acceptable amount

5. Use biological control if necessary and available

6. Use pesticides as a last resort

❖ Such systems can be effective with minimum impact on the environment

❖ Pests reduce productivity in agricultural ecosystems (weeds compete with crop plants for water, minerals etc, insect can damage leaves of crops needed for photosynthesis/ in direct competition eating the crops themselves)

❖ Monoculture- a large area of land in which only 1 crop is grown, this enables pests to spread rapidly, pests may cause disease, animals become unfit for human consumption as do not grow rapidly which will lead to reduced productivity

❖ The effect of productivity is to balance the cost of pest control with the benefits it brings the problem is that the farmer has to balance the demand for cheap food while still making a living and the conservation of natural habitats so we can have food in the future.

5.6 Intensive Rearing of Domestic Livestock

❖ Designed to produce the maximum yield of meat, eggs and milk at the lowest cost possible

❖ They do this by using methods to convert the smallest amount of food energy into the greatest amount of animal mass

❖ They do this my minimising there energy loss by keeping them in confined spaces to increase energy conversion rate, it does this because:

1. Movement is restricted so less energy is used in muscle contraction

2. Environment can be kept warm so not used to maintain body heat

3. Feeding can be controlled for maximum growth

4. Predators are excluded so no loss to other organisms in food web

❖ Other means include selective breeding of animals to produce varieties that are more efficient at converting food into body mass and using hormones to increase growth rates

❖ Main features of intensive rearing are:

1. Efficient energy conversion

2. Low cost

3. Worst tasting food

4. Less land is used leaving more natural habitats

5. High density animal population more at risk to spread of disease but easier to isolate if this happens

6. Animals are regularly given antibiotics to prevent spread of disease

7. Over use of drugs lead to antibiotic resistance and can also alter the flavour of food or pass into the foods then into humans affecting their health

8. Maintains a higher level of animal welfare but can lead to aggressive behaviour from being in unnatural conditions

9. Produces large concentrations of waste in a small area rivers and ground waters may become polluted, pollutant gases can be dangerous and smell, larger have own waste facilities

10. Reduced genetic diversity due to selective breeding

11. High energy-conservation rates due to use of fossil fuels, CO2 levels released increased global warming

Economic and environmental issues

❖ Economic- desire for cheap food conflicts with the conservation of the environment

❖ Environment- reduced species diversity due to:

1. removal of hedges and woodland

2. creation of monocultures

3. filling in ponds and draining marshes and other wetlands

4. over-grazing of land preventing regeneration of woodland

❖ Indirect effect to reduce species diversity-

1. use of pesticides and inorganic fertilisers

2. escape of farm wastes into water courses

3. absence of crop rotation leading to poor soil structure

❖ Conservation techniques include:

1. maintaining existing hedgerows

2. planting hedges as field boundaries

3. maintaining existing ponds and where possible creating new ones

4. leaving wet corners of fields rather than draining them

5. planting native trees in low species diversity areas

6. reduce use of pesticides using biological control where possible

7. using organic rather than inorganic fertilisers

8. using crop rotation with a nitrogen fixing crop

9. creating natural meadows and using hay for silage

10. leaving the cutting of verges and field edges until after flowering and seeds have dispersed

6. Nutrient Cycles

6.1 The carbon cycle

❖ Shows how carbon moves through living organisms and the non-living environment. 1. Carbon (Co2) is absorbed by plants by photosynthesis, becoming carbon compounds in plants.

2. Carbon is passed along the food chain through consumption.

3. When organisms die, carbon compounds are digested by microorganisms and returned to the air as they carry out respiration.

4. If any dead organic matter ends in places where there aren’t any decomposers, their carbon compounds can be turned into fossil fuels. The carbon in these fossil fuels is released when they are burnt for fuel.

❖ CO2 concentration falls during the day as it is removed by plants as they carry out photosynthesis. It then increases at night as it’s no longer being removed by photosynthesis but all organisms continue to respire and add CO2.

❖ CO2 concentration decreases in the summer in some climates as it is when light intensity is greatest – more photosynthesis can occur. More CO is removed as more plants are photosynthesising.

6.2 The greenhouse effect and global warming

❖ The greenhouse effect is a natural process that occurs all the time without it the average temperature on earth would be -18 degrees Celsius, the gases that surround the earth in the atmosphere trap the heat from the sun keeping it warm at 17 degrees Celsius

The most important greenhouse gas is CO2 because it remains in the atmosphere for much longer than other greenhouse gases, 50-70% of global warming is due to CO2.

Human activities increases the amount of carbon dioxide in the atmosphere enhancing the greenhouse effect

Methane is also a greenhouse gas which is produced when decomposers break down the dead remains of organisms or then microorganisms in the intestines of primary consumers digest the food that has been eaten

Global warming is where the mean temperature of the Earth has increased

❖ Consequences of global warming:

1. Melting of polar ice caps which could cause the extinction of some plants and animals and also a rise in sea level

2. Rise in sea level could cause flooding, salt water would extend further up rivers making cultivation of crops difficult

3. Higher temperatures and less rainfall lead to failure of crop growth in some areas, distribution of wild plants change and so animal distribution would change

4. Greater rainfall and storms in some areas cause change in distribution of plants and animals

5. Life-cycles and populations of insect pests would change as they adapt, tropical diseases could then spread further up north as the insects migrate

❖ Could also benefit as increased rainfall would fill reservoirs, increased temperature grow crops in places where originally too cold, rate of photosynthesis increase, may be possible to harvest twice a year

6.3 The Nitrogen Cycle

❖ Plants and animals need nitrogen to make proteins and nucleic acids (DNA/RNA) ❖ Although the atmosphere has 78%, can't use it in that form, need saprobiotic bacteria to convert it into nitrogen compounds first. ❖ Nitrogen Cycle includes: 1. Nitrogen fixation 2. Ammonification 3. Nitrification 4. Denitrification.
1. Nitrogen Fixation (Can also happen when lightning passes through the atmosphere) ❖ Nitrogen gas in the atmosphere is turned to ammonia by nitrogen-fixing bacteria ❖ Free-living nitrogen fixing bacteria reduce gas to ammonia which is then used to manufacture amino acids. Nitrogen rich compounds released when they decay ❖ Mutualistic bacteria e.g. Rhizobium is found in root nodules of leguminous plants. e.g. peas, beans ❖ They form a mutualistic relationship with the plants- they provide the plant with nitrogen compounds and the plant provides them with carbohydrates
2. Ammonification ❖ Nitrogen compounds from dead organisms are turned into ammonium compounds by decomposers ❖ Animal waste also contains compounds and are turned into ammonium

3. Nitrification

❖ This is the conversion of ammonium ions to nitrate ions by nitrifying bacteria, to be used by the plant.

❖ Firstly nitrifying bacteria oxidise ammonium ions to nitrite ions (N02-)

❖ Secondly other nitrifying bacteria oxidise nitrite ions to nitrate ions (N03-) ❖ The bacteria require oxygen, so soil with lots of air spaces by ploughing and good drainage so air spaces are not filled with water is needed.
4. Denitrification ❖ Nitrates in the soil are converted into nitrogen gas by denitrifying bacteria they use nitrates in the soil to carry out respiration and produce nitrogen gas ❖ Happens under anaerobic conditions - no oxygen e.g. waterlogged soil. ❖ Parts of the cycle can be carried out artificially on an industrial scale. Haber process produces ammonia from atmospheric nitrogen to make fertilisers.

6.4 Use of Natural and Artificial Fertilisers

❖ All plants need mineral ions, especially nitrogen

❖ Intensive food production makes large demands on soil because mineral ions are continually being taken up by crops grown there

❖ In natural ecosystems the minerals are returned when the plant is broken down my microorganisms on its death

❖ In agricultural the plants are harvested and transported for consumption and are rarely returned to the same area, making it necessary to replenish these minerals or it will become a limiting factor to the plants growth

❖ To do this 2 different types of fertilisers are added:

1. Natural (organic) fertilisers- consist of dead and decaying plants and animals as well as animal waste (manure and bone meal)

2. Artificial (inorganic) fertilisers- mined from rocks and deposits then converted into different forms and blended to give the appropriate amount of mineral needed for the land (NKP fertilisers)

❖ Plants need these minerals for grown e.g. nitrogen to make proteins and DNA, when available plants are more likely to develop earlier, grow taller and have a greener leaf area, this increases rate of photosynthesis and so increases productivity

6.5 Environmental consequences of using nitrogen fertilisers

❖ Reduced species diversity can occur- nitrogen rich soils favour the growth of grasses, nettles and other rapidly growing species which causes more competition for other species which then die out and so reduces species diversity. ❖ Leaching- when water soluble compounds in soil are washed away, e.g. by rain / irrigation systems, into nearby ponds and lakes. ❖ If nitrogen fertiliser is leached it can cause eutrophication: 1. Nitrates leached from fertilised fields stimulate growth of algae in ponds etc. 2. Large amounts of algae block light from reaching plants below 3. Plants die as they are unable to photosynthesise 4. Bacteria feed on the dead plant matter 5. Increased numbers of bacteria reduce the oxygen concentration in water by carrying out aerobic respiration 6. Fish etc. die as there isn't enough dissolved oxygen ❖ Organic manures, animal slurry, human sewage, ploughing old grass land and natural leaching can also cause eutrophication but artificial is main cause.

7. Ecological Succession

1. Succession

❖ Succession --> term to describe changes taking place over time ❖ 1st Step is --> colonisation of an inhospitable environment by organisms --> called pioneer species --> their features suit them because they: 1. rapidly germinate seeds 2. reach isolated areas easily 3. have the ability to photosynthesise 4. have the ability to fix nitrogen 5. have tolerance to extreme conditions ❖ Succession takes place in a series of stages --> at each stage certain species can be identified which change the environment --> therefore the environment becomes more suitable for other species --> these other species out compete current species --> this forms a new community ❖ During any succession, common features are: 1. the non-living environment becomes less hostile which leads to --> 2. greater number and variety of habitats which produce --> 3. increased biodiversity which lead to --> 4. more complex food webs 5. increased biomass

7.2 Conservation of Habitats

Conservation is the management of the Earth's natural resources so that maximum use of them can be made in the future.
Main reasons for conservation: ❖ Ethical- other species have existed longer and so should be allowed to co-exist ❖ Economic- long term productivity is greater if ecosystems are maintained in their natural balanced state ❖ Cultural and aesthetic- Variety add interest to our every day lives
Ways to manage succession:
1. Animals left to graze on land, so larger plants can't establish themselves and vegetation kept low
2. Managed fires are lit, after fires secondary succession will occur on the moorland, so the pioneer species growing back will be the species that is being conserves e.g. heather

8. Inheritance and Selection
8.1 Studying inheritance ❖ Dominant Allele: allele that is always expressed in the phenotype. ❖ Recessive Allele: allele that is expressed in the phenotype in the absence of a dominant allele. ❖ Co-dominance: both alleles are dominant and are expressed in the phenotype. ❖ Genotype: constitution of an organism comprising all the genes possessed by an individual. ❖ Phenotype: characteristics of an organism, often visible, resulting from the genotype and the effects of the environment. ❖ Heterozygous: having two different alleles for a given gene. ❖ Multiple Alleles: when a gene has more than 2 allelic forms ❖ Homozygous: having two dominant/recessive alleles present for a given gene.

8.2 Monohybrid Inheritance

Representing genetic crosses

❖ Choose a single letter to represent each characteristic

❖ Choose the first letter of one of the contrasting features

❖ Choose the letter in which the higher and lower case forms differ in shape as well as size so they cannot be confused

❖ Higher letter represents dominant gene, lower for recessive gene

❖ State the gametes produces by each parent, indicating meiosis

❖ Use a punnet square to show the result of the random crossing of gametes, label male and female

❖ State the phenotypes of each different genotype and indicate the number of each type. Always write the higher case letter first

Inheritance of pod colour in peas

Another example of a monohybrid cross is a person with Huntington disease, this is a dominant gene: coded for by protein Huntington

A similar cross can be done for cystic fibrosis which is the recessive gene coded for by the protein CFTR

8.3 Sex Inheritance and Sex Linkage

❖ Sex is determined by chromosomes rather than genes

❖ As females on have x and males have either x or y males determine the sex of a child (xx for female, xy for male)

Sex Linkage- Haemophilia

❖ A gene that is carried on the x or y chromosome is said to be sex linked

❖ Carried on the X chromosome, males either have the disease or don’t but women can be carriers

❖ Males can therefore only obtain a disease from their mothers as the gene is not carried on the y chromosome they inherit from their fathers but the x chromosome from the mother, if she does not have the disease but the son does then she would be a carrier and so heterozygous for the condition

8.4 Co-dominance and Multiple Alleles

❖ Co-dominance occurs when both alleles are dominant so both are expressed within the phenotype

❖ E.g. a plant that codes for red and white flowers, both are dominant so the colours would be:

1. Homozygous for red = red

2. Homozygous for white = white

3. Heterozygous = pink

❖ C= colour and then R= red and W= white:

Multiple alleles

❖ Inheritance of the ABO blood group is an example of this

❖ 3 genes carried on the I (immunoglobulin gene), which lead to the different production of different antigens on the surface of red blood cells

8.5 Allelic Frequency and Population Genetics

❖ Gene pool- all of the genes of all the individuals of a population at any one time

❖ Allelic frequency- the number of times a gene appears within the gene pool

Example:

❖ Cystic fibrosis- C- dominant allele which codes for normal production of mucus

❖ c- Recessive allele which codes for thinker production of mucus and cystic fibrosis

❖ Pairs of alleles for cystic fibrosis have 3 different combinations:

1. CC- heterozygous dominant

2. cc- Homozygous recessive

3. Cc / cC- Heterozygous

❖ The total number of alleles is said to be 1.0, in a population if no one had cystic fibrosis then the frequency of the gene c would be 0.0 whereas the frequency of the gene C would be 1.0. If everyone was heterozygous then the frequency of C or c would be 0.5

The Hardy-Weinberg Principle

❖ A mathematical equation can be used to calculate the frequency of alleles

❖ Principle states that the proportion of dominant and recessive alleles stays the same from generation to generation if:

1) No mutations arise

2) The population is isolated

3) There is no selection

4) The population is large

5) Mating within the population is random

❖ Let the frequency of allele A = p and the frequency of allele a = q

❖ P + q = 1.0

❖ 4 possible arrangements (AA, Aa, aA and aa) the frequency of all 4 added together = 1.0

❖ Therefore:

If 1 in 25000 people have a (recessive) then aa= 1/25000 therefore q squared = 0.00004

If p + q = 1.0 and q is then equal to 0.00063, p = 0.9937

To calculate heterozygous you then use 2pq = (2 x 0.9937 x 0.0063) = 0.0125

So 125 in 10 000 carry the allele for the character

8.6 Selection

Reproductive success and allele frequency

❖ All organisms produce more offspring then can be supported

❖ Despite overproduction most population remain constant

❖ There is competition between members of a species to survive

❖ Within the population thee will be a wide variety of alleles in the gene pool

❖ Some will possess the genes which make them better able to survive

❖ These individuals will obtain he available resources and grow more rapidly as a result will have more successful breeding and offspring

❖ The more successful then pass on their genes

❖ The ones with advantageous alleles will then compete better and will reproduce

❖ The number of individuals with the advantageous alleles will increase

❖ Over time, the frequency of the allele increases

❖ The advantages will vary due to environment

Types of selection

❖ Selection is the process in which organisms that are better adapted will survive and breed

❖ Different environmental conditions favour different characteristics within a population

❖ Selection that favours individuals in one direction from the mean population is called directional selection

❖ Selection that favours the mean population is called stabilising selection

Directional selection

❖ Environmental conditions change so phenotype needed to survive changes

❖ New individuals become more adapted to survive at one end of the spectrum and so over time the mean changes to suit the new phenotype

❖ This results in phenotypes at one extreme being favoured and the other being favoured against

Stabilising selection

❖ Environmental conditions remain the same

❖ Mean are favoured, extremes are favoured against

❖ Eliminates extremes

8.7 Speciation

❖ Speciation is the evolution of new species from an existing one

❖ Species- a group of individuals with similar genes that can produce fertile offspring

❖ If 2 populations become isolated in some way, there is no longer a flow of alleles, the environment with each group may differ and so one type of allele frequency may change in time the gene pools will become so different that they are no longer the same species

❖ Geographical isolation:

❖ Occurs when a physical barrier prevents 2 populations from breeding with one another e.g. rivers, mountains and deserts

Example in a forest

[pic]

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Continued adaptations
Leads to evolution
Of new species Y and Z

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