Topic 3: Leaves

Question 1

Describe photosynthesis

Answer 1

the process by
which plants synthesise carbohydrates from raw
materials using energy from light

Question 2

State the word equation for photosynthesis

Answer 2

carbon dioxide + water → glucose + oxygen
in the presence of light and chlorophyll

Question 3

What is chlorophyll?

Answer 3

Chlorophyll is the protein found within chloroplasts that catalyses the reaction. It is also what causes plants to be green!

Question 4

Chlorophyll function?

Answer 4

chlorophyll transfers energy from light
into energy in chemicals, for the synthesis of
carbohydrates

Question 5

State the balanced chemical equation for
photosynthesis

Answer 5

6CO2 + 6H2O → C6H12O6 + 6O2

Question 6

Outline the subsequent use and storage of the
carbohydrates made in photosynthesis,

Answer 6

(a) starch as an energy store
(b) cellulose to build cell walls
(c) glucose used in respiration to provide energy
(d) sucrose for transport in the phloem
(e) nectar to attract insects for pollination

Question 7

Explain the importance of nitrate ions and magnesium ions

Answer 7

a) nitrate ions for making amino acids, Stunted growth
Leaves (usually near growing tip) start to turn yellow

(b) magnesium ions for making chlorophyll, Yellowing between the veins of leaves (known as chlorosis) due to lack of chlorophyll production

Question 8

Identify and explain the limiting factors of
photosynthesis in different environmental
conditions

Answer 8

When a process depends on two or more factors (variables), the rate of that process is determined by the factor which is in shortest supply.

The main limiting factors are
Light intensity
Carbon dioxide concentration
Temperature

Question 9

Leaf features and how these features are adaptions for photosynthesis

Answer 9

most leaves have a large surface area
and are thin - aid diffusion.

Question 10

Investigate the need for chlorophyll, light
and carbon dioxide for photosynthesis, using
appropriate controls

starch v glucose

Answer 10

Plants make glucose but leaves cannot be tested for its presence as the glucose is quickly used, converted to other substances, transported, or starch.
Starch is in chloroplast where photosynthesis occurs so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising.

Question 11

Investigate and describe the effect of light and
dark conditions on gas exchange in an aquatic
plant using hydrogen carbonate indicator solution

DAY V NIGHT

Answer 11

The ratio of photosynthesis to respiration in plants changes over the day cycle
Plants are constantly respiring and releasing carbon dioxide
Plants only photosynthesise during the day when sunlight is available, taking in carbon.
During the day plants photosynthesise faster than they respire, resulting in a net intake of carbon dioxide
During night plants respire more than they photosynthesis, resulting in a net release of carbon dioxide
Hydrogen carbonate indicator is a pH indicator that changes colour depending on the pH of a solution
Carbon dioxide is acidic.
Higher carbon dioxide concentration = more acidic

Question 12

5 Uses of glucose in plants to remember!

Answer 12

1. Glucose is commonly stored in plants as starch (long chains of glucose)
2. Glucose can be used in cellulose to build cell walls
3. Glucose can be used for respiration
4. Glucose can be converted in to sucrose and transported through phloem vessels from source to sink
5. Glucose can be converted in to nectar and used to attract pollinators

Question 13

Parts of the leaf

Answer 13

Guard cells
Waxy Cuticle
Epidermal cells
Palisade mesophyll- chloroplast + vacuole
Spongy mesophyll
Vascular bundle - xylem + phloem
Stomata

Question 14

Guard cells function

Answer 14

Open and close stomata

Question 15

Waxy cuticle function

Answer 15

Allows light to pass through whilst protecting leaf surface

Question 16

Epidermal cells function

Answer 16

offers protection but thin to allow light through

Question 17

palisade cell function

Answer 17

Contain many chloroplasts
Packed tightly together
Large surface area
Large vacuole pushes chloroplast to edges of cell
Thin cell walls to aid gaseous exchange
ALL OPTIMISED FOR LIGHT EXPOSURE

Question 18

Spongey mesophyll function

Answer 18

Irregular shaped
Fewer chloroplasts
Smaller than palisade cells
Spaced out with air pockets in between
OPTIMISED FOR ALLOWING GASES TO PASS EASILY

Question 19

Vascular bundle (xylem and phloem) functions

Answer 19

Xylem - transport of water and mineral ions, and support.
Phloem - transport of sucrose and amino acids

Question 20

Xylem vessel structure in relation to their function

Answer 20

Thick walls with lignin
No cell contents
Cells joined end to end with no cross walks to form a continuous tube

Question 21

Root hair cells feature

Answer 21

Root hairs increases surface area, therefore increasing the rate of osmosis / diffusion

Question 22

Water trip through plant

Answer 22

soil -> root hair cell -> root cortex cells -> xylem -> mesophyll layer -> air pockets -> stomata -> atmosphere

Question 23

transpiration definition

Answer 23

Transpiration is the loss of water vapor from leaves

Question 24

How does transpiration affect water concentration in leaf?

Answer 24

Causes water concentration in leaf to decrease

Water moves by osmosis down water potential gradient from soil to xylem vessels then up the plant to the leaves

Question 25

What causes plants to wilt?

Answer 25

if more water evaporates from a plant than can be absorbed from the soil, the plant cells will become flaccid, causing the plant to wilt

Question 26

How does cohesion and adhesion allow water to move up xylem vessels?

Answer 26

Cohesion of water and adhesion to the walls of the xylem vessel allows water to move up xylem vessels, like water up a straw

Question 27

Effects of limiting factors on transpiration

Answer 27

temperature increases the rate until another factor is the limiting factor

humidity decreases the rate of transpiration because it decreases the leaf’s water concentration

Higher wind speed = faster evaporation of water out of stomata = faster rate of transpiration

Question 28

Describe translocation

Answer 28

the movement of
sucrose and amino acids in phloem from sources
to sinks

Question 29

What are sources and sinks?

Answer 29

sources as the parts of plants that release
sucrose or amino acids
sinks as the parts of plants that use or store
sucrose or amino acids

Question 30

Explain why some parts of a plant may act as a
source and a sink at different times

Answer 30

phloem can transport these nutrients in any direction.
carbs in plants: produced by photosynthesis as glucose, transported as sucrose, used for respiration

Question 31

Concentrations (1, high to 5, low) of CO2 vs hydrogen carbon indicator colour and the condition of the plant. (investigating light)

Answer 31

1. yellow
2. orange
   respiration > photosynthesis, lower pH, more acidic
3. red
   respiration = photosynthesis
4. magenta
   5.purple
   respiration < photosynthesis, higher pH, more alkaline

Question 32

What’s a limiting factor?

Answer 32

A limiting factor is something that is in short supply that restricts a process

Question 33

Effect of light intensity on photosynthesis.

Answer 33

The rate of photosynthesis increases with light intensity
When the intensity of light increases to a certain point, photosynthesis cannot go any faster.

Question 34

Effect of carbon dioxide concentration on photosynthesis.

Answer 34

Increasing the CO2 concentration, increases rate of photosynthesis
BUT, there is a maximum rate

Question 35

Effect of temperature on photosynthesis

Answer 35

Too much heat damage enzymes and causes them to denature
Too much heat also evaporates water out of leaves and forces stomata to close
Too little heat can reduce enzymes reaction rate by reducing number of collisions between the enzyme’s active site and substrate