Photosynthesis

Question 1

why is photosynthesis important

Answer 1

• plants use the chemical energy they get from photosynthesis to synthesis large organic molecules, they form the building block of living cells from simple inorganic molecules such as water and carbon dioxide this is called autotrophic nutrition

Question 2

What are organisms that photosynthesise called

Answer 2

Photoautotrophs

Question 3

Write down the general equation for photosynthesis

Answer 3

6CO2 + 6H20 + energy from photons = C6H12O6 + 6O2

chlorophyll over the equals sign

Question 4

What is a photon

Answer 4

A photon is a particle of light, each photon contains an amount of energy

Question 5

What is the main product of photosynthesis

Answer 5

the main product is a monosaccharide sugar this can then be converted back to a diasaccharide for transport

Question 6

what is carbon fixation

Answer 6

this is the process by which carbon dioxide is converted into sugars
- the carbon synthesising all types of organic molecules is provided by carbon fixation

Question 7

What kind of reaction is carbon fixation

Answer 7

• it is an endothermic reaction so needs energy

- also needs electrons, the addition of electrons is a reduction reaction

Question 8

What does carbon fixation do

Answer 8

it helps regulate the concentration of carbon dioxide in the atmosphere and oceans

Question 9

What do plants do in respiration

Answer 9

• they oxidise the organic molecules that have previously synthesised by photosynthesis and stored releasing chemical energy
• they oxidise glucose and other organic molecules to produce carbon dioxide and water and release chemical energy

Question 10

what are heterotrophs

Answer 10

These are non-photosynthetic organisms that obtain energy by digesting complex organic molecules of food to smaller molecules that they can use as respiratory substances,

Question 11

What kind of reaction is respiration

Answer 11

• it is exothermic as it releases chemical energy and drives the organisms metabolism

Question 12

Write out the equation for respiration

Answer 12

C6H12O6 + 6O2 = 6H20 + 6CO2 + energy

Question 13

How do photosynthesis and respiration work together

Answer 13

• they are important for maintaining the atmosphere
• photosynthesis removes carbon dioxide from the atmosphere and releases oxygen whereas aerobic respiration does the opposite

Question 14

What is the compensation point

Answer 14

• This is when photosynthesis and respiration happens at the same rate therefore there is not net gain or loss of carbohydrate

Question 15

Whats the compensation period

Answer 15

this is the time taken for the plant to reach its compensation point

Question 16

What can affect the compensation period

Answer 16

• different for different plant species
• shade plants can utilise light of lower intensity than sun plants can
• when exposed to light after being in darkness shade plants reach their compensation point quicker than sun plants which require a higher light intensity to reach their maximum photosynthesis rate

Question 17

What is the granum

Answer 17

• this is the inner part of chloroplast made of stacks of thylakoid membranes where the light dependent stage of photosynthesis takes place

Question 18

What is a stroma

Answer 18

• this is the fluid-filled matrix of chloroplasts where the light dependent stage of photosynthesis takes place

Question 19

Describe a chloroplast

Answer 19

• disc shaped and around 2-10 micrometres long
• they are surrounded by a double membrane, the envelope with an intermembrane space of width 10-20 nanometres between the inner and outer membrane
• outer membrane is highly permeable

Question 20

Where does the first stage of photosynthesis take place

Answer 20

• it takes place in the grana

Question 21

Describe the granum

Answer 21

• chloroplasts have three distinct membranes, these are the outer, inner and thylakoid which means there are three separate internal compartments these are the intermembrane space, stroma and the thylakoid space
• the thylakoids within a granum may be connected to thylakoids within another granum by intergranal lamellae
• thylakoid membrane of each chloroplast is less permeable and folds into flattened disc-like sacs called thylakoids that form sack
• each thylakoids is called a granum and one granum may contain up to 100 thylakoids

Question 22

what is there a huge surface area for in the chloroplast

Answer 22

• the distribution of photosystems that contain the photosynthetic pigments that trap sunlight energy
• the electron carriers and ATP synthase enzymes that are needed to convert that light energy into ATP

Question 23

What holds the photosystems in place

Answer 23

proteins that are embedded in the thylakoid membranes

Question 24

What is the grana surrounded by and why

Answer 24

it is surrounded by the stroma so the products of the light dependent stage can easily pass to the stroma to be used in the light independent stage

Question 25

Describe what the stroma is used for

Answer 25

- contains the enzymes which are needed to catalyse the reactions of the light-independent stage of photosynthesis - contains starch, grains, oil droplets, small ribosomes similar to those found in prokaryote cells and DNA - loop of DNA contains genes that code for some of the proteins needed for photosynthesis these are assembled at the chloroplast ribosomes

Question 26

What is a photosynthetic pigment

Answer 26

- this is a pigment that absorbs specific wavelengths of light and traps the energy associated with the light, such as pigments include chlorophyll a and b, carotene and xanthophyll

Question 27

How do photosynthetic pigments work

Answer 27

- energy associated with the wavelengths of light is captured is funneled down to the primary pigment reaction centre consisting of a type of chlorophyll at the base of the photosystem

Question 28

What are the two types of chlorophyll

Answer 28

- chlorophyll a | - chlorophyll b

Question 29

Describe chlorophyll a

Answer 29

- there are two types, P680 and P700 - They are both blue-green and are both situated at the centre of photosystems, both absorb red light and have different absorption peaks - P680 - found in photosystem II and peak 680nm - P700 - found in photosystem I and peak 700nm - also absorbs some blue light with wavelength of around 440nm

Question 30

Describe chlorophyll b

Answer 30

- absorbs blue light of wavelengths 400-500 nm, and around 640 nm - appears yellow green

Question 31

describe carotenoids

Answer 31

- absorb blue light of wavelength 400-500 nm | - reflect yellow and orange light

Question 32

Describe Xanthophylls

Answer 32

- absorb blue and green light of wavelengths 375-550 nm | - they reflect yellow light

Question 33

What are the factors affecting photosynthesis

Answer 33

- light intensity - carbon dioxide concentration - temperature - water stress

Question 34

Describe how light intensity affects photosynthesis and what effect does it have on the Calvin cycle

Answer 34

- light provides the energy to power the first stage of photosynthesis and produce ATP and reduced NADP needed for the next stage - also causes the stomata to open for gaseous exchange, this causes transpiration and the uptake of water - DRAW THE GRAPH - as light intensity decreases photosynthesis decreases - GP cannot be reduced to TP - TP levels fall and GP accumulates - if TP levels fall RuBP cannot be regenerated

Question 35

Describe how carbon dioxide affects photosynthesis and how does it affect the Calvin cycle

Answer 35

- if carbon dioxide concentration increases the rate of photosynthesis increases - RuBP cannot accept it and accumulates - GP cannot be made - Therefore TP cannot be made

Question 36

Describe how temperature affects photosynthesis and the Calvin cycle

Answer 36

- from low temperatures to temperatures of around 25-30 degrees if plants have enough water and carbon dioxide and sufficient light intensity the rate of photosynthesis increases as temperature increases - at temperatures above 30 degrees for most plants, growth rates may reduce due to photorespiration; oxygen completes with carbon dioxide for the enzyme RuBisCO's active site reducing the amount of carbon dioxide being accepted by RuBP and subsequently reducing the quantity of GP and therefore TP being produced, due to the lack of TP being produced this means that RuBP cannot be regenerated - at temperatures above 45 degrees enzymes involved are denatured reducing the concentrations of GP and TP therefore eventually RuBP as it cannot be regenerated due to lack of TP

Question 37

Describe how water stress affects photosynthesis

Answer 37

if not enough water is available to the plant than - the roots cannot take up enough to replace the water lost in transpiration - cells loose water and become plamolysed - plant roots produce abscisic acid that when translocated to leaves it causes stomata to close reducing gaseous exchange - tissues become flaccid and leaves wilt - the rate of photosynthesis greatly reduces