Unit 3 - Key Area 1 - Food supply, plant growth and productivity.

Question 1

What is food security?

Answer 1

The ability of human populations to access food of sufficient quality and quantity.

Question 2

What must food production be?

Answer 2

Must be sustainable, must not degrade natural resources such as water and soil nutrients on which agriculture depends.

Question 3

Why is there an increased demand for food production?

Answer 3

An increasing human population has lead to an increase in demand for food production.

Question 4

What is sustainable food production?

Answer 4

Organisms are not harvested at a faster rate than they can reproduce.

Question 5

What is agricultural production?

Answer 5

It is crop production of the likes of cereals, roots, legumes and potatoes.

Question 6

What is crop yield?

Answer 6

Crop yield is a measure of how much crop is harvested, compared with how much was planted.

Question 7

How do fertilisers increase crop yield?

Answer 7

Fertilisers add nutrients back into the soil that may have been limiting plant growth, increasing food production.

Question 8

How do pesticides increase crop yield?

Answer 8

Pesticides reduce the number of weeds which compete with crops and pests that damage/eat crops.

Question 9

How does biological control increase crop yield?

Answer 9

A natural predator, parasite or pathogen of a crop pest is introduced to decrease crop numbers.

Question 10

How does planting genetically modified cultivars of crop plants increase crop yield?

Answer 10

Crops can be genetically modified to be pest resistant, disease resistant, higher yielding and tolerant to a wider range of conditions.

Question 11

What is a cultivar?

Answer 11

‘Cultivated varieties’ Groups of plants that have been selected for desirable characteristics.

Question 12

What is different about livestock production?

Answer 12

It is possible to raise livestock in habitats which are unsuitable for growing crops.

Question 13

Why does livestock production produce less food per unit area?

Answer 13

There is a loss of energy between trophic levels (one stage in a food chain).

Question 14

What is the rate of food production dependent on?

Answer 14

Food production is dependent on factors which limit the rate of photosynthesis.

Question 15

Factors which limit the rate of photosynthesis and therefore food production?

Answer 15

Light intensity, temperature and carbon dioxide concentration.

Question 16

What happens when white light hits a leaf?

Answer 16

Majority is absorbed by photosynthetic pigments in the chloroplasts, the rest is transmitted or reflected.

Question 17

The four main photosynthetic pigments in the chloroplasts?

Answer 17

Chlorophyll a, chlorophyll b, carotene and xanthophyll. (Carotene and xanthophyll are the carotenoids.) Each pigment will absorb different wavelengths of light.

Question 18

How to calculate the RF value?

Answer 18

Distance travelled by pigment from origin / distance travelled by solvent from origin.

Question 19

What does an absorption spectra show?

Answer 19

Shows which wavelengths of light are absorbed most strongly by a photosynthetic pigment, each wave has a different absorption spectrum.

Question 20

What wavelengths do chlorophyll a and chlorophyll b absorb best?

Answer 20

Blue and red.

Question 21

What is the role of the carotenoids?

Answer 21

They extend the range of wavelengths of light that can be absorbed and the pass energy onto the chlorophyll for photosynthesis.

Question 22

What is an action spectra?

Answer 22

Shows the effect of different wavelengths of light on the rate of photosynthesis. It is evidence of the importance of photosynthetic pigments in photosynthesis.

Question 23

Photosynthesis - Stage 1 - Light dependent stage ~ part one.

Answer 23

The photosynthetic pigments absorb different wavelengths of light. All energy absorbed by carotenoids is passed to the chlorophyll in the thylakoids of the chloroplast.

Question 24

Photosynthesis - Stage 1 - Light dependent stage ~ part two.

Answer 24

All this energy excites electrons in the chlorophyll molecules. The high energy electrons are captured by a primary electron acceptor and are transferred to an electron transport chain in the thylakoid membrane. As electrons pass through the chain they release energy.

Question 25

What is energy produced used for?

Answer 25

1. By ATP synthase to produce ATP.
2. For photolysis (the splitting of water into oxygen and hydrogen)

Question 26

What happens to the ATP produced in the light dependent stage?

Answer 26

The ATP produced in the light dependent stage is transferred to the carbon fixation stage. The hydrogen is transferred to the coenzyme NADP, forming NADPH to be used in the carbon fixation stage. The oxygen is released as a waste product.

Question 27

Light dependent stage summary.

Answer 27

1. Light energy is absorbed by chlorophyll.
2. Excited electrons captured by the primary electron acceptor.
3. Electrons are transferred through the electron transport chain releasing energy.
4. Some energy is used to generate ATP.
5. Some energy is used to split water (photolysis).
6. Oxygen is released as a waste product, hydrogen is transferred to NADP.

Question 28

Photosynthesis - Stage 2 - Carbon fixation stage (Calvin cycle).

Answer 28

This stage occurs in the stroma of the chloroplast. The carbon fixation reactions are catalysed by specific enzymes and so this stage is temperature dependent.

Question 29

Stages of the Calvin cycle.

Answer 29

1. Carbon dioxide is fixed to ribulose biphosphate (RuBP) to form two molecules of 3-phosphoglycerate (3PG). the reaction is catalysed by RuBisCO.
2. 3-phosphoglycerate is combined with hydrogen from NADP and is phosphorylated from ATP to produce glyceraldehyde-3-phosphate (G3P).
3. Some glyceraldehyde-3-phosphate molecules are used to synthesise glucose.
4. Some glyceraldehyde-3-phosphate (G3P) molecules are used to regenerate ribulose biphosphate (RuBP).

Question 30

Fates of glucose.

Answer 30

1. Used as a respiratory substrate.
2. Synthesise into a starch for energy storage.
3. Synthesised into cellulose as a structural carbohydrate.
4. Passed onto other biosynthetic pathways leading to the formation of a variety of metabolites such as DNA, proteins and fats.