2.6 Photosynthesis

Question 1

photosynthesis

Answer 1

an endothermic reaction where energy is transferred from the environment to the chloroplasts by light from the sun.
Glucose is made.

Question 2

glucose

Answer 2

made during photosynthesis
can be stored as starch, used straight away in respiration or used to make cellulose

Question 3

stomata

Answer 3

holes on the underside of the leaf which open and close to allow for gas exchange
control the loss of water by closing during the night but open during the day thanks to guard cells

Question 4

spongy mesophyll

Answer 4

a tissue found in plant leaves that is specialised for gas exchange by having air spaces that allow the diffusion of gasses to happen quicker

Question 5

waxy cuticle

Answer 5

on top of the upper epidermis that is insoluble so waterproofs the leaf and reduces evaporation of water but transparent to allow light to pass through for photosynthesis

Question 6

palisade mesophyll

Answer 6

a tissue found in the plant leaves that are specialised to carry out photosynthesis by being vertically packed to capture more sunlight and to store more chloroplasts

Question 7

What other molecules is glucose used to make in plants?

Answer 7

Carbohydrates:
starch for storage
sucrose for transport
fructose, found in fruits
cellulose makes cell walls

DNA, made of nucleotides

Amino acids, joined together to make proteins

Lipids, e.g. to make cell membrane and oils in seeds

Chlorophyll

Question 8

Why do plants require nitrates (NO3-)?

Answer 8

Required to make amino acids (and so
proteins) and nucleic acids (DNA and RNA)

Question 9

What is the symptom of nitrates deficiency?

Answer 9

stunted growth

Question 10

Why do plants require magnesium (Mg)?

Answer 10

Required to make chlorophyll

Question 11

What is the symptom of magnesium deficiency?

Answer 11

yellow leaves

Question 12

Why do plants require phosphates (PO4 3-)?

Answer 12

Required to make nucleic acids (RNA and
DNA)
part of cell membrane

Question 13

What is the symptom of phosphates deficiency?

Answer 13

Poor root growth
purple younger leaves

Question 14

What is a limiting factor?

Answer 14

The factor which is in shortest supply is called the limiting factor.

Question 15

What 3 factors can limit the rate of photosynthesis?

Answer 15

light intensity
temperature
carbon dioxide

Question 16

How can carbon dioxide concentration affect photosynthesis?

Answer 16

adding more carbon dioxide the reaction
can happen faster, as there are more
molecules to collide with enzymes

Question 17

How can light intensity affect the rate of photosynthesis?

Answer 17

adding a brighter light we increase the
rate photosynthesis, as there is more
energy for the reaction to occur

Question 18

How can temperature affect the rate of photosynthesis?

Answer 18

Increasing temperature speeds up the reaction.
This is because the enzymes and substrates have more kinetic energy and collide more often.
However, at high temperatures the rate of
photosynthesis decreases and the reaction stops.
This is because the enzymes carrying out the
stages of photosynthesis have been denatured.

Question 19

upper epidermis

Answer 19

upper epidermis is transparent, allowing light to penetrate to the mesophyll

Question 20

xylem

Answer 20

xylem transports water (absorbed in the roots) into the leaves. This then provides a short distance for water to diffuse into the photosynthesising cells

Question 21

phloem

Answer 21

The phloem vessels transport sugars made in photosynthesis to other parts of the plant

Question 22

Explain the steps required to test a leaf for the presence of starch

Answer 22

1. Heat a leaf in boiling water for one minute
2. Transfer the leaf to a test tube containing ethanol and place in the hot water (that is in a beaker)
3. Soften the leaf by transferring it to the beaker of hot water
4. Place the leaf on a white tile and cover in iodine solution
   5.Observe any colour change - blue/black shows starch is present

Question 23

How can the starch experiment show the conditions needed for photosynthesis?

Answer 23

• To show that light is required, one leaf is covered with foil (or part of the leaf is covered)
  –> only the leaves (parts of the leaf) exposed to light will produce starch and turn black
• To show chlorophyll is required, a variegated leaf, in which the white parts of the leaf
  lacks chlorophyll is used
  –> starch is only produced in the areas that were green
• To show carbon dioxide is required one leaf of a plant is enclosed in a conical flask (or
  plastic bag) containing soda lime to absorb the carbon dioxide and this leaf is compared
  to another enclosed in a flask but without the soda lime
  –> Only the leaf that had access to
  carbon dioxide produces starch.