Food supply, plant growth, and productivity

Food security

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

Why is there a concern for food security?

There is a growing human global population which increases the demand

What two things must food production be?

Sustainable and not degrade the natural resources in which agriculture depends on

Sustainability

Something that’s guaranteed over a long period of time

Where does most human food come from?

A small number of plant crops

What four crops does most human food come from?

• Cereals

• Legumes

• Potatoes

• Roots

What is food production (agriculture) dependent on?

The factors that control photosynthesis and plant production

What is the solution to the problem - the area to grow crops is limited?

Replace existing crop plants when higher yielding cultivars

What is the solution to the problem - shortage of mineral elements or water?

Increase the supply of fertilisers or use a sprinkler system

What is the solution to the problem - pests (eg. fungi or Insects)?

Use fungicides or insecticides

What is the solution to the problem - competition from weeds?

Use herbicides

What four things do plant breeders seek to develop in their crops?

• Ability to thrive in particular environmental conditions

• Disease and pest resistance

• High nutritional values

• Physical characteristics suited to harvesting and rearing

Why is food production (agriculture) dependent on photosynthesis?

Produces obtain their energy from the sun and this is then passed onto animal consumers along the food chain

Diagram: food chain

Diagram: food security

Why do livestock produce less food per unit area than plants?

90% of energy is lost at each tropic level, whereas only 10% is passed along

Which food chains are more efficient?

Shorter ones

What two things explain why livestock is sometimes farmed rather than crops?

The climate might be too harsh and the landscape might not be suitable

Example: why is livestock sometimes farmed rather than crops?

If the environment is too hilly or rocky

What must a plant do to be productive?

Photosynthesis as rapidly as possible

Photosynthesis

The process by which green plants absorb light energy to make glucose

Why is the rate of photosynthesis of crop plants important?

The greater the rate of photosynthesis, the greater the rate of plant growth and therefore the higher the yield of the crop

What are two factors that affect the rate of photosynthesis of a plant?

The concentration of pigments in the leaves and the size of the leaf

What is the first thing to happen in photosynthesis?

Light is absorbed by the plant leaves

Visible light

The name given to the light from the sun or light bulbs that is made up of all the colours of the rainbow

What are the three fates of light when hitting a leaf?

• Absorption

• Reflection

• Transmission

A pigment

A substance which absorbs visible light

What determines the colour of pigments?

The light/wavelength they don’t absorb

What are the four pigments in plant leaves?

• Chlorophyll A

• Chlorophyll B

• Carotene

• Xanthrophyll

What determines colours?

Wavelengths of lights

What is the technique that separates photosynthetic pigments?

Chromatography (TLC)

What is an advantage of plants having carotenoids?

The total quantity of light absorbed is greater than it would have been if only one pigment was absorbed

What do carotenoids do?

Pass the energy to chlorophyll (A and B)

What are the two pigments known as carotenoids?

Carotene and xanthrophyll

Absorption spectrum

This shows how much light of each wavelength is absorbed by the different plant pigments

What apparatus is used to measure the degree of absorption by the different plant pigments?

A spectrometer

Action spectrum

This shows the effectiveness of different wavelengths of light at brining about photosynthesis

What does the close correlation between the action and absorption spectrum show?

The leaf pigments absorb the wavelengths of light that are the most effective at bringing about photosynthesis

What is stage one of photosynthesis?

The light dependent stage

What is stage two of photosynthesis?

The Calvin cycle

What are the four stages of the light dependent stage?

1. Light energy, absorbed by pigments, excited electrons in the pigment molecules

2. These high-energy electrons are transferred through an electron transport chain and pump hydrogen ions across the membrane. The return flow of hydrogen ions drives ATP synthase

3. Rotation of ATP synthase produces ATP

4. Energy is also used to split water into hydrogen ions and oxygen (photolysis). Oxygen is evolved (removed) and hydrogen ions bind to the coenzyme NADP to form NADPH

What two things are required for the Calvin cycle from the light dependent stage?

ATP and the hydrogen ions held in the coenzyme NADP

What are the three stages of the Calvin cycle?

1. Carbon dioxide enters the cycle and binds to RuBP (Ribulose Biphosphate). This reaction is controlled by the enzyme RuBisCO

2. The intermediate produced (3-phosphoglycerate/3GP) is phosphorylated by ATP and combines with hydrogen ions (from NADPH). This forms glyceraldehyde-3-phosphate (G3P)

3. G3P is used to synthesis glucose and to regenerate RuBP

Diagram: the light dependent stage

Diagram: the Calvin cycle

What are the four possible fates of glucose at the end of photosynthesis?

• Respiration

• Synthesised into cellulose as a structural carbohydrate

• Synthesised into starch as a storage carbohydrate

• Other pathways (to form DNA, fat, proteins, etc)