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

Explain why food security is of increasing concern

Answer 2

The increasing human population is leading to a demand for increased food production. So a higher quantity of food is needed.

Question 3

what does agricultural production depend on

Answer 3

the factors that control photosynthesis and plant growth

Question 4

what are the factors that control plant growth

Answer 4

-breeding of higher yielding cultivars (cultivated varieties),

-use of fertiliser,

-protecting crops from pests,

-diseases and competition.

Question 5

why do livestock produce less food per unit area than crop plants

Answer 5

due to loss of energy between trophic levels

Question 6

what is visible light in relation to photosynthesis

Answer 6

Visible light is the part of the spectrum which drives photosynthesis

Question 7

what are the two fates of light hitting a leaf

Answer 7

-Light energy not absorbed by the leaf pigments is transmitted or reflected

-Light energy is absorbed by photosynthetic pigments to generate ATP and for photolysis (first stage of photosynthesis)

Question 8

function and colour of pigment chorophyll A

Answer 8

initiates the light reactions / photolysis

blue / green

Question 9

function and colour of pigment chlorophyll B

Answer 9

an accessory pigment

yellow / green

Question 10

function and colour of pigment xanthophyll

Answer 10

an accessory pigment; a carotenoid

yellow

Question 11

function and colour of pigment carotene

Answer 11

an accessory pigment; a carotenoid

orange

Question 12

how does chlorophyll A initiate light reactions

Answer 12

The three accessory pigments capture light energy then pass energy on to chlorophyll A.

Chlorophyll A is the only pigment that can initiate the light reactions

Question 13

The proportion of a particular wavelength absorbed by a pigment can be measured using a…

Answer 13

spectrophotometer (or spectroscope).

Question 14

Explain why black bands appear in the spectrograph for the extracted leaf pigments

Answer 14

They are the wavelengths/colours of light that have been absorbed by the leaf pigments

Question 15

what is an absorption spectrum

Answer 15

a graph which plots a pigment’s visible light absorption

Question 16

what is an action spectrum

Answer 16

the rate of photosynthesis over all visible wavelengths

Question 17

how are pigments involved in photosynthesis

Answer 17

Each pigment absorbs a different range of wavelengths of light.

Carotenoids extend the range of wavelengths absorbed and pass the energy to chlorophyll for photosynthesis.

Question 18

what happens inside thylakoids

Answer 18

light energy is transformed to chemical energy in the form of the products ATP and NADPH

Question 19

where does photolysis, the light-dependent reaction take place

Answer 19

in the membrane of thylakoids in the chloroplasts

Question 20

describe Photolysis, the light-dependent reaction

Answer 20

-Light energy strikes the thylakoid membranes and is absorbed by the pigment molecules. Absorbed light energy excites electrons in the pigment molecule

-The transfer of these electrons through the electron transport chain releases energy to generate ATP by ATP synthase

-Energy is also used for photolysis, in which water is split into oxygen, which is evolved (released out of leaf), and hydrogen ions, which are transferred to the coenzyme NADP

Question 21

what products do the light reactions produce

Answer 21

ATP [Used in the calvin cycle]

NADPH [Used in the calvin cycle]

oxygen – diffuses out of the chloroplast, out of the mesophyll cell then out through the stoma

Question 22

where does The Carbon fixation stage (Calvin Cycle) take place

Answer 22

in the stroma of the chloroplast

Question 23

At which point in the calvin cycle is the enzyme RuBisCO required

Answer 23

1

Question 24

At which point in the calvin cycle is hydrogen required

Answer 24

2

Question 25

what do carotenoids in green plants do

Answer 25

They extend the range of wavelengths of light absorbed and pass energy onto chlorophyll

Question 26

describe the carbon fixation stage (the calvin cycle)

Answer 26

-the enzyme RuBisCo fixes carbon dioxide (which diffused into the leaf-chloroplast) by attatching it to ribulose bisphosphate (RuBP), producing 3-phosphoglycerate (3PG)

-the 3PG is phosphorylated by ATP and combines with hydrogen ions from NADPH to form glyceraldehyde-3-phosphate (G3P)

-G3P is used to regenerate RuBP and for the synthesis of glucose

-glucose may be used as a respiratory substance, synthesised into starch or cellulose or passed to other biosynthetic pathways. these biosynthetic pathways can lead to the formation of a variety of different metabolites such as DNA, protein and fat