C20 - Photosynthesis and Environmental Management Flashcards Preview

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Flashcards in C20 - Photosynthesis and Environmental Management Deck (95):

What's succession?

The gradual change in community over time.
The natural development of an ecosystem.

During succession, organisms within the environment/ecosystem change its abiotic enable better adapted organisms to colonise.


What's primary succession?

When organisms colonise a lifeless habitat.


What's secondary succession?

When organisms re-colonise a devastated ecosystem.


What's a climax community?

A stable community which has no more succession and contain high biodiversity.


What are pioneers?

Organisms/species which are very specialised and are the first to inhabit an area.

E.g. With sand dunes, the pioneer species is marram grass.


What are abiotic factors?

Non-living factors e.g. Salinity, temperature, pH etc.


What are biotic factors?

Living factors e.g. Disease, predators, competition etc.


What's a xerophyte?

Species of plant adapted to survive in an arid environment, adapted to conserve water.


What's a halophyte?

A species of plant that grows in waters of high salinity in contact with saline water.


What's deflected succession?

When the formation of a climax community is prevented by human activities e.g. Land management (e.g. Mowing, coppicing and agriculture).

Deflected succession results in a phagioclimax community.


How are forests managed?

Deciduous woodland makes up the majority of the community but many native deciduous trees have been removed and replaced with non-native trees to meet timber and fuel demands.

Remaining woodland is managed by coppicing and rotation so different stages of succession are always present.


How do ecologists monitor biodiversity?

By sampling parts of the ecosystem.


How does sample size affect results?

Larger samples are more representative of the whole ecosystem.

This increases validity but can be limited by time, money, labour, equipment etc.

Bias should also be avoided.


What are the two methods for assessing biodiversity?

Random sampling and systematic sampling.


What's random sampling?

Location of the sample points is decided by generating random numbers which are used as grid coordinates.
A quadrat is placed at the coordinates and the species present are observed, identifies and counted to calculate a percentage cover.

It avoids bias but can produce unrepresentative data of the ecosystem, especially is the area is large.


What are the two types of systematic sampling?

Stratified sampling and transects.


What's a stratified sample?

When the ecosystem is divided into smaller areas based on the distribution of habitats. This is a more representative method.


What's a transect?

Belt transect- when quadrants are placed at regular intervals along a straight line transect.

Line transect - only what touches the line is measured.

It's usually used where a correlation may exist between an abiotic variable.


Where do light dependent reactions take place in the chloroplasts?

The grana / thylakoid membranes.


Where do light independent reactions take place in the chloroplast?



What are grana?

Stacks of thylakoid membranes within chloroplasts.


What are thylakoids?

Flattened membrane discs stacked on top of one another to form grana.


What’s the stroma?

The fluid filled matrix containing all enzymes required for light independent photosynthesis.


How are chloroplasts adapted for their role (5)?

1) The inner membrane has transport proteins and is less permeable than the outer membrane. This allows control of substances entering the stroma.

2) Stacked thylakoids (producing grana) increases surface area.

3) Photosynthetic pigments are organised in photosystems to maximise light absorption efficiency.

4) Grana are surrounded by the stroma so products from the LDR can pass directly to enzymes catalysing LIDR (independent).

5) Chloroplasts contain their own DNA and ribosomes. They can produce some of their own photosynthetic proteins rather than importing them from the cell cytoplasm.


What energy conversions take place in chloroplasts in the light dependent stage?

Light energy to chemical energy (in photosystems).

Kinetic energy of proton flow through ATP-synthase to form ATP (chemical energy)


What is the role of photosystems do in LDR of photosynthesis?

They convert light energy into chemical energy


What do the photosystems do in LDR of photosynthesis?

Chlorophyll b molecules and accessory pigments in light-harvesting complexes absorb photons.

This energy is funnelled down to a reaction centre at the heart of a photosystems.
Electrons in 2 chlorophyll a molecules in the reaction centre are excited and rise to a higher E level. These high-E electrons are transferred to nearby molecules, known as electron acceptors.

The e- are passed through several electron carriers via redox reactions. (The Electron Transport Chain). The e- lose energy so energy is released.

The energy is used to pump proteins across the thylakoid membrane into space within the thylakoids, producing a proton gradient.


What is photophosphorylation?

The harnessing of light energy to produce ATP.

After use of the photosystems, the protons that accumulated inside the thylakoids move back across the membrane down the concentration gradient.

Chemiosmosis occurs as protons flow through the ATP synthase.

The ATP synthase converts kinetic to chemical energy and bonds ADP and Pi to form ATP.


What’s photolysis?

The splitting of water into H+ ions, electrons and oxygen by the enzyme in photosystems II.


What occurs during photolysis?

Water is split into H+ ions, electrons and oxygen.

2H2O —> 4H+ + 4e- + O2


What happens to the products of photolysis?

H+ ions are pumped into the thylakoid space, enabling ATP synthase to produce ATP via chemiosmosis.
They can also reduce NADP to NADPH in the stroma in the LIDR stage.

Electrons replace those lost by the oxidation of the chlorophyll a in photosystems II.

Oxygen is a waste product and will either diffuse out of the leaves through stomata or be used by plant cells in aerobic respiration.


What is produced at the end of the light dependent stage of photosynthesis?

ATP and NADPH is produced on the stromal side of the thylakoid membranes.

Both are necessary for the light independent stage.


What is the other name for the light independent stage of photosynthesis?

The Calvin Cycle


What is the role of CO2 in the Calvin cycle?

CO2 is fixed in the stroma of chloroplasts.

It acts as the carbon source for all photosynthetic organisms.


What is the role of ATP in the Calvin cycle?

ATP that is generated in the light dependent stage provides the energy to drive the carbon fixation reactions and the production of carbohydrates.

3 molecules of ATP are used for every turn of the Calvin cycle.


What is the role of NADPH in the Calvin cycle?

NADPH provides the reducing power (donating the hydrogen from the LDR) to enable the conversion of glycerate-3-phosphate (GP) to triode phosphate (TP).

The H from NADPH is added to GP to form TO and ATP provides the energy for this.

2 NADPH molecules are used for every turn of the cycle.


What occurs in the Calvin cycle?

1) CO2 diffuses through the stomata, plasma membrane, cytoplasm and chloroplast into the stroma.

2) The enzyme RuBisCo catalyses the reaction between RuBP (ribulose bisphosphate) and CO2.

3) The 5C RuBP molecule and the single C atom in CO2 combine to produce 2 molecules of GP (3C).

4) ATP and NADPH are used to reduce GP to another 3C molecule, TP.

5) NADP has been regenerated and returns to the light-dependent stage, where it can be reduced again by accepting further H+ ions.

6) Some TP is converted to molecules that can be used by the plant e.g. glucose.

7) The majority of TP is used to regenerate RuBP and continue the cycle. Additional ATP is needed.


How is GP (glycerate-3-phosphate) made?

By the carboxylation of RuBP (combining with CO2).


What are the different products from GP in 3 different reactions?

- It can be reduced to TP, which requires ATP and NADPH and continues the Calvin cycle.

- Conversion to acetyl CoA which gets converted to fatty acids.

- Formation of amino acids. This requires mineral ions. (Nitrates provide N, sulfates provide S)


How is TP formed?

By the reduction of GP in the Calvin cycle.


What are the (5) different products from TP?

- Most of the TP is used to regenerate RuBP and continue the Calvin cycle.

- 2 TP molecules can join to form 6C sugars e.g. glucose and fructose

- Glucose and fructose can react to produce sucrose (disaccharide)

- Glucose molecules can react to form polysaccharides e.g. amylose, amylopectin and cellulose

- A single TP molecule can be converted to glycerol, which can react with fatty acids to form triglycerides

TP can also be used to make amino acids.


What are photosynthetic pigments?

Intrinsic proteins found in the thylakoids membrane of chloroplasts.


What happens in the light dependent stage of photosynthesis?

Chlorophyll b, arranged in light harvesting complexes, funnels photons through the complex where it gets absorbed by chlorophyll a molecules in the centre.

Electrons are then excited to a higher energy level by light photons. As the electrons pass along the ETC, they lose energy each time (and energy is released).

Photophosphorylation occurs (chemiosmosis).
The energy released is used to pump protons from the stroma to the thylakoid space across the thylakoid membrane.

This sets up a concentration gradient in the thylakoid space (higher concentration in the space).

Protons will diffuse down the gradient through ATP synthase which generates ATP.

At the end of ETC, e- combine with protons in the stroma and NADP forms NADPH.


What gets produced in the LDR stage of photosynthesis?

NADPH and ATP which are used in the Calvin cycle.

O2 which is waste and leaves the plant.

H+ ions and e- which get reused.


What are the similarities in ETC between photosynthesis and respiration?

Proton pumping


Use redox reactions

Occur in membranes

Use electron carrier proteins

Produce ATP

Release H+ and e- at the end of the chain


What are the differences in ETC between photosynthesis and respiration?

NADP for photosynthesis, NAD for respiration

Final electron acceptor is O2 in respiration, NADP in photosynthesis

Photolysis in plants

Photosynthesis requires light

Occurs in cristae in respiration, thylakoids in photosynthesis


What occurs during the Calvin cycle?

The enzyme, RuBisCo triggers the carboxylation of RuBP

RuBP and CO2 produce a very unstable 6C molecule that breaks down immediately & forms 2 3C molecules of glycerate 3 phosphate (GP).

GP is reduced by ATP and reduced by NADP from LDR reactions to form 2 3C molecules of triode phosphate (TP).

Some TP is used to build carbohydrates and complex molecules.
Most is recycled to make more RuBP.


What is used in each cycle of the Calvin cycle?

3 ATP used

2 NADP used


What are the limiting factors of photosynthesis?

- intensity
- wavelength
- duration





How does light intensity affect photosynthesis?

It limits the rate at which ATP and NADPH are produced in light dependent reactions.

At low light intensities, GP concentrations will rise.
RuBP and TP concentrations will decrease due to insufficient ATP and NADPH to convert GP to TP and TP to RuBP.


How does light wavelength affect photosynthesis?

Different ranges of wavelengths are absorbed by photosynthetic pigments.
Some plants may not receive all wavelengths equally.


How does light duration affect photosynthesis?

Number of daylight hours will determine the amount of sunlight a plant can absorb.


How does CO2 affect photosynthesis?

Optimum CO2 concentration for high rate of photosynthesis is 0.1%.

At low concentrations, RuBP will accumulate and GP formation will be limited.


How does temperature affect photosynthesis?

Higher temperature provides more kinetic energy for the molecules involved in photosynthetic reactions, therefore rate increases.

Higher temperatures slow rate as it’ll cause enzymes e.g. RuBisCo to denature.


How does temperature affect the light dependent and independent stages of photosynthesis?

It has little effect in the LDR as few enzymes are needed for this stage, except for photolysis.

However, each light independent reaction is catalysed by an enzyme, so temperature will have a bigger effect on this stage.


How does pH affect photosynthesis?

Changes in pH can cause proteins to denature e.g. the enzyme RuBisCo.
This reduces photosynthesis rate.


What’s the compensation point?

When the rate of respiration is equal to the rate of photosynthesis.

This means CO2 and O2 intake and release are equal.

It’s usually reached at dawn and dusk.


How can hydrogen-carbonate indicator be used to identify photosynthesis and respiration?

It can be placed in a small container with a sample of plant.

It’s originally red.
If concentration of CO2 increases, pH will decrease and the indicator will turn yellow.

If concentration of CO2 decreases, pH increases and the indicator turns purple.


How does hydrogen-carbonate indicator change with CO2 concentration?

It’s originally red.

If concentration of CO2 increases, pH will decrease and the indicator will turn yellow.

If concentration of CO2 decreases, pH increases and the indicator turns purple.


What’s ammonification?

When saprotrophic microorganisms (decomposers) break down proteins, nucleic acids and vitamins from dead organisms and nitrogenous waste e.g. urea.

Ammonia and ammonium ions are produced and added to soil.


What are the (4) main stages in the nitrogen cycle? (Nitrogen recycling)


Nitrogen fixation




What’s nitrogen fixation?

When atmospheric nitrogen is converted into nitrogen-containing compounds e.g. ammonia, by nitrogen fixing bacteria.


How do nitrogen fixing bacteria work?

The fix nitrogen for plants using the enzyme nitrogenase (and receive carbohydrates from the plant).

It takes about 16 moles ATP to reduce 1 mole nitrogen to ammonia.


Where are nitrogen fixing bacteria found?

Some are free living or in soils.

Others have mutualistic relationships with plants e.g. rhizobium lives in nodules on the roots of leguminous plants e.g. beans.


What occurs during nitrification?

Nitrifying bacteria (nitrosomonas) convert ammonia ions into nitrite ions (NO2-).
These are then converted to nitrate ions by bacteria (nitrobacter).

Plants take in nitrogen as nitrate ions (NO3-) by root hair cells via active transport.


What happens during denitrification?

It’s a reduction reaction.

Bacteria cause nitrates to be converted back into nitrogen gas.
This occurs in anaerobic, waterlogged conditions lacking in oxygen.


What does a food chain show?

The transfers of energy between organisms within an ecosystem.


What’s a tropic level?

The level at which a particular organism feeds in a food chain.


What’s a producer?

An autotrophic organism that converts light energy to chemical energy.


What’s the primary consumer?

An organism gaining organic molecules and chemical energy from the consumption of producers.


What’s a secondary consumer?

Carnivores that eat primary consumers


What are tertiary consumers?

Carnivores eating secondary consumers


Which trophic level of food pyramids has the most chemical energy?

The producers.
Energy is lost in every stage of the food chain


Why is it more energy-efficient to farm fish than cattle?

Fish are ectotherms and rely on external sources of heat to regulate body temperature therefore less energy is used to generate heat. Cattle are endotherms.


What are the components to the structure of a ruminant stomach?

Small intestines


What happens as ruminants consume and digest food?

Food travels down the oesophagus and into the rumen.
The rumen contains microorganisms that are able to digest cellulose. Ruminants do not produce the cellulase enzyme that is capable of digesting cellulose therefore they absorb little glucose directly from their diets.

Instead, microorganisms in the rumen and reticulum breakdown cellulose and other carbohydrates into disaccharides and monosaccharides. Other bacteria convert these molecules into fatty acids.

The abomasum acts like a human stomach by secrete hydrochloric acid and protease enzymes, which digest bacterial proteins into amino acids.


What does NPP stand for?

Net primary productivity
(The mass per unit area per year)

NPP = GPP - respiration loss


What’s NPP?

Net primary productivity
(The mass per unit area per year)

NPP = GPP - respiration loss


What’s GPP?

Gross primary productivity - the energy fixed by photosynthesis over the course of a year.


How can farmers manipulate light to increase energy available to consumers?

- Plants can be grown under light banks in greenhouses to provide constant, optimal light intensity and duration.

- Timing of sowing maximises the leaf area present during optimum conditions for photosynthesis over the summer months.

- Sowing density is chosen to prevent one plant overshadowing another.


How can farmers manipulate temperature to increase energy available to consumers?

Greenhouses provide regulated, warm temperatures.


How can farmers manipulate water to increase energy available to consumers?

- Crops can be irrigated to ensure that water isn’t a limiting factor.

- Drought resistant varieties are artificially selected and GM drought resistant crops have been developed.


How can farmers manipulate nutrients to increase energy available to consumers?

- Farmers rotate crops (alternate crops in each field).

- Nitrate levels in soil can be replenished by growing a nitrogen fixing crop, e.g. beans, within the rotational cycle or by the application of fertilisers in either organic or inorganic form.


How can farmers manipulate competition to increase energy available to consumers?

- Herbicides are sprayed to kill weeds that compete with crops.

- GM crops resistant to herbicides.


How can farmers manipulate pests to increase energy available to consumers?

- Pesticides are used which maintains leaf area for photosynthesis.

- GM pest resistant plants are developed by inserting the bacterial Bt gene into their genomes. It codes for a protein toxic to crop eating insects.


How can farmers manipulate disease to increase energy available to consumers?

Fungicides are sprayed to kill fungal pathogens on plants.


How can secondary productivity (of farming ecosystems) be manipulated to improve efficiency of energy transfers? (5)

- Treatment with antibiotics reduces the energy expenditure of farm animals’ immune systems by reducing bacterial infections.

- More energy can be channelled into growth by limiting the movement of farm animals. This is called ‘zero grazing’.

- The maintenance of a constant temperature reduces energy expenditure or thermoregulation, allowing more energy to be used for growth.

- Selective breeding produces breeds of animals capable of increased productivity.

- Animals can be harvested before reaching adulthood. Juvenile animals invest a greater percentage of energy into growth than adults.


What is the opposite of intensive farming?

Extensive farming


What’s biological control?

When natural predators are used instead of pesticides.


What are the advantages of increasing secondary productivity? (Farming)

Increased output / yield

More profitable


Occupies less land

Cheaper for consumer

Less likely to catch disease

Efficient energy transfer

Waste can be used to produce methane (biofuel)


What are the disadvantages of increasing secondary productivity? (Farming)

Can lead to antibiotic resistance

Cruel / animals have poor quality of life

Food wastage

Lower quality meat

Selective breeding can cause health problems

Shorter life span for animals

Leakage of waste which may lead to eutrophication


What does DCPIP do when investigating factors affecting photosynthesis?

It’s a blue dye that acts as an electron acceptor.
It becomes colourless when it accepts electrons and is reduced.

This allows it to be used to detect reducing agents produced by light dependent reactions of photosynthesis.


What (2) methods are used to investigate factors affecting photosynthesis?




What equipment is used in a photosynthometer?

Water bath
Water or potassium hydrogen carbonate solution
Capillary tube
Plastic tubing

It’s used to measure (the rate of) oxygen production in aquatic plants.


Where does photolysis occur?

Photosystem II