photosynthesis

Question 1

what does life depend on

Answer 1

life depends on continuous transfer of energy

Question 2

what is the site of photosynthesis

Answer 2

the leaf is the main photosynthetic structure

chloroplasts in leaf are where photosynthesis takes place

Question 3

what is the structure of the leaf

Answer 3

photosynthesis takes place largely in the leaf are adapted to bring together and produce three raw materials of photosynthesis (water, CO2, light) and remove its products (CO2 & glucose)

Question 4

what are the adaptions of the leaf

Answer 4

• large surface area - absorbs as much sunlight as possible

an arrangement of leaves on plants - minimises overlapping and so avoids the shadow of one leaf by another

• thin
  most light is absorbed in the first few micrometers
• transparent cuticles & epidermis
  lets light through to the photosynthetic mesophyll cells beneath

-numerous stomata
for gaseous exchange so that the mesophyll cells are only a short pathway from one

Question 5

what is the simplified equation for photosynthesis

Answer 5

6CO2 + 6H2O → C6H12O6 + 6O2 + 6H2O

photosynthesis produces the oxygen we breath by releasing it from water

Question 6

what are the main stages of photosynthesis

Answer 6

1. capturing of light energy: by chloroplast pigment such as chlorophyll
2. the light-dependent reaction: in which some of the light energy absorbed is conserved in chemical bonds
3. the light-independent reaction: in which these protons (hydrogen ions) are used to produce sugars and other organic molecules

Question 7

what is the structure and role of chloroplasts in photosynthesis

Answer 7

photosynthesis takes place within cell organelles called chloroplasts (vary in shape & size) but is typically disc shape
inside the chloroplast membranes are two distinct regions:
-the grana
-thylakoid -light dependant stage
-the stroma - light-independent

Question 8

what is the light-dependent reaction

Answer 8

involves the capture of light whose energy is uses two purposes

to add inorganic phosphate (Pi) molecules to ADP thereby making ATP

to split water into H+ ions (protons) and OH- ions. As the splitting is caused by light, it is known as photolysis

Question 9

what is oxidation

Answer 9

when substance gains oxidation/ loses hydrogen the process is called oxidation
the substance had been oxidised

when a substance is oxidized, it loses electrons

Question 10

what is reduction:

Answer 10

when a substance is reduced, it loses O2/ gains hydrogen

when a substance is reduced, it gains electrons

Question 11

what happens during the light-dependent stage of photosynthesis

Answer 11

1. light enters thylakoid and excites 2 electrons from chlorophyll molecule (oxidation). The proton pump gains these electrons
2. the reduced proton pump can actively transport proton (H+) from the stroma into the thylakoid space
   This creates an electrochemical gradient
3. the electrons are transported from the proton pump (oxidation) to the electron carrier (reduction)
4. the protons diffuse down an electrochemical gradient through ATP synthase. This allows the enzyme to catalyse ADP +Pi to ATP
5. 2e- and an H+ are transferred to a coenzyme called dehydrogenase to make reduced NADP (NADPH) ready to be used in the Calvin Cycle. This occurs with the help of an enzyme
6. We replenish the electrons by using water in a process called phtolysis

Question 12

what is photolysis

Answer 12

the loss of electrons when light strikes a chlorophyll molecule leaves it short of electrons

these electrons must be replaced
The replacement electrons are provided from water molecules that are split using light energy

Question 13

what is the equation for the photolysis of water

Answer 13

2H2O 🠪 4H +4e +O2

protons, electrons and oxygen

Question 14

what are the protons (from photolysis) used for

Answer 14

the protons out of the thylakoid space through the ATP synthase channels and are taken up by an electron carrier called NADP

this becomes reduced NADP and is the main product of the light-dependent stage and enters the LIGHT INDEPENDENT REACTIONS taking with it the electrons from the chlorophyll molecules

Question 15

why is reduced NADP important

Answer 15

it furthers the potential source of chemical energy to the plant

Question 16

what happens to the oxygen produced during the photlysis of water

Answer 16

O2 by product from photolysis is used in respiration or diffuses out of the leaf (as a waste product)

Question 17

where does the light - dependent reaction take place

Answer 17

thylakoids of chloroplasts

Question 18

what are the adaptions of the chloroplast

Answer 18

• thylakoids membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the light - dependent reaction
• network of proteins in the grana hold chlorophyll in a very precise manner that allows maximum absorption
• granal membranes have ATP synthase channels within them, which allows establishment of a proton gradient

chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the light - dependent reaction

Question 19

what is the light - independent reaction

Answer 19

products of the light - dependent reaction of photolysis:

ATP and reduced NADP are used to reduce glycerate 3 - phosphate in the second stage of photosynthesis

it does not require light

Question 20

where does the light - independent reaction take place

Answer 20

takes place in the stroma of the chloroplast

Question 21

what are the stages of the Calvin cycle (the light independent reaction)

Answer 21

1. CO2 from the atmosphere diffuses into the leaf through stomata and dissolves in the water around the wall of the mesophyll cells

It then diffuses through the cell - surface membrane, cytoplasm and chloroplast membranes into the stroma of the chloroplast

2. in the stroma CO2 reacts with ribulose bisphosphate this reaction is catalysed by rubisco
3. the reaction produces 2 of the 3 - carbon glycerate phosphate (GP)
4. Reduced NADP is used to reduce glycerate 3 - phosphate to triose phosphate (TP) using energy supplied by ATP
5. Some triose phosphate molecules are converted to organic substances that the plant need
   e. g.
   - starch
   - cellulose
   - lipids
   - glucose
   - amino acids
   - nucleotides e.t.c

7.most triose phosphate molecules are used to regenerate ribulose bisphosphate using ATP from the light - dependent reaction

Question 22

where does the light - independent reaction take place

Answer 22

takes place in the stroma of the chloroplasts

Question 23

what are the adaptions of the stroma that allows it to carry out the light independent reaction

Answer 23

• fluid of stroma contains all the enzymes needed to carry out the light - independent reaction

stromal fluid is membrane - bound in the chloroplast which means a chemical environment which has and substrates can be maintained within it - as distinct from the environment of the cytoplasm

the fluid surrounds the grana and so the produces of he light-dependent reaction the grana can readily diffuse into the stroma

• contains both DNA and ribosomes so it can quickly and easily manufacture some of the proteins involved in the light - independent reaction

Question 24

what are the factors that limit photosynthesis

Answer 24

• CO2 concentration
• light intensity
• temperature
• chlorophyll
• water availability

Question 25

describe the relationship between light intensity and photosynthesis

Answer 25

as light increasesthe rate therefore increases.

This means that light is the limiting factor.
When light increases but the rate remains constant, it means that another factor is limiting photosynthesis

(this applies for CO2

Question 26

describe the relationship between light intensity and photosynthesis

Answer 26

as temperature increases, rate therefore increases.

This means that temp is the limiting factor due to the increased kinetic energy of enzymes e.g. rubisco

The optimum temp sis then reached and therefore another factor is limiting e.g. light/CO2

as temp increases, rate decreases as enzymes have denatured

the graph looks like a bell curve

Question 27

hexose sugars

Answer 27

the calvin cylce needs to turn six times to make one hexose sugar

The reason for this is that three turns of the cycle produces six molecules of triose phosphate (because two molecules of TP are made for every one CO2 molecule used)
Five out of six of these TP molecules are used to regenerate ribulose biphosphate. This means that for three turns of the cycle only one TP is produced that’s used to make a hexose sugar.

Hexose sugar has six carbons though, so two TP molecules are needed to form form one hexose sugar. This means the cycle must turn sux times to produce two molecules of TP that can be used to make one hexose sugar

Six turns of the cycle need 18 ATP and 12 reduced NADP from the light - dependent reaction

Question 28

how are lipids made from the calvin cycle

Answer 28

they are made using glycerol, which is sythesised from triose phosphate, and fatty acids, which is sythesised from glycerate 3 - phosphate

Question 29

how are amino acids made from the Calvin cycle

Answer 29

some amino acids are made form glycerate 3 phosphate

Question 30

how are carbohydrates made from the Calvin cycle

Answer 30

hexose sugars are made from two triose phosphate molecules

Question 31

light intensity and photosynthesis

Answer 31

only certain wavelengths of light are used for photosynthesis

The photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb the red and blue light in sunlight