3.1) Food Supply, Plant Growth and Productivity

Question 1

• State the term ‘food security’

Answer 1

• Food security
  ➞ the ability of human populations to access food of sufficient quality and quantity 🍉

Question 2

• Explain the importance of sustainable food production.

Answer 2

• The rapid increases in human population and concern for food security has lead to a demand for increased food production.
• Food production must be sustainable and not have a negative impact on the ecosystem and natural resources.

Question 3

• Describe the 5 factors which affect plant growth and agriculture production.

Answer 3

1. Control of limiting factors
2. Use of fertilisers for nutrients
3. Planting strains of crops that have a higher yield
4. Removing competition from weeds and diseases by using pesticides, fungicides and herbicides
5. Developing pest/disease-resistant crops

Question 4

• Compare the differences in food production between livestock and plants.

Answer 4

• Livestock produces less food per unit area than crop plants due to loss of energy between trophic levels (90%)
  ➞ Livestock production is often possible in habitats unsuitable for growing crops.

Question 5

• Describe 3 ways light can behave when interacting with leaves.

Answer 5

1. ABSORBED
   ➞ by photosynthetic pigments to generate ATP and for photolysis
2. TRANSMITTED
   ➞ through the leaf
3. REFLECTED
   ➞ off the leaf.

Question 6

• Describe the function of pigments in relation to photosynthesis and give examples.

Answer 6

• Pigments are chemicals found within the chloroplasts which absorb light energy and convert it into chemical energy
• The principal pigments are chlorophyll A and chlorophyll B
  ➞ which mainly absorb light in red and blue wavelengths of light.
• Plants also contain carotenoids (carotene and xanthophyll)
  ➞ which absorb light from other regions of the spectrum, extending the range of wavelengths absorbed and pass energy on to chlorophyll for photosynthesis.

Question 7

• Describe the functions of the absorption spectra and action spectra.

Answer 7

1. ABSOPRTION SPECTRA
   ➞ shows the wavelengths of light absorbed by the different pigments in a leaf (chlorophyll A/B and carotenoids)
2. ACTION SPECTRA
   ➞ shows how effective the different wavelengths of light are at photosynthesis

Question 8

• Describe and explain the process of photolysis.

Answer 8

1. Absorbed light energy excites electrons in the pigment molecule.
   ➞ Transfer of these electrions through the electron transport chain releases energy to generate ATP by ATP synthase.
2. Energy is also used for photolysis, in which water is split into oxygen and hydrogen.
   * Oxygen:
   ➞ diffuses out of the leaf into the atmosphere
   * Hydrogen:
   ➞ then becomes bonded to the coenzyme NADP to form NADPH and is transferred to the Calvin Cycle along with ATP.

Question 9

• Describe and explain the process of the Calvin Cycle.

Answer 9

1. The enzyme RuBisCO fixes carbon dioxide by attaching it to RuBP (ribulose biphosphate) to produce 3PG
2. The 3PG produced is phosphorylated by ATP and combined with hydrogen ions from NADPH to form G3P
3. G3P is used to regenerate RuBP and for the synthesis of glucose.

Question 10

• What are the uses of glucose?

Answer 10

1. respiratory substrate (energy source) ⚡
2. synthesised into starch or cellulose 🫙
3. passed to other biosynthetic pathways 🌱