Plant Physiology

Question 1

Explain what a de starched leaf is

Answer 1

A leaf that has used up all its starch storage
Due to an inability to photosynthesize and produce glucose to make more starch
Which would have been caused by a factor such as a lack of carbon dioxide or light

Question 2

Give a criticism of the statement
that chlorophyll is needed for photosynthesis using the starch experiment on a variegated leaf

Answer 2

The white part of the leaf may have given a negative test but this doesn’t mean it didn’t photosynthesize, because it may have and the starch made may have been transported elsewhere in the plant

Question 3

How is starch made in a plant

Answer 3

From glucose, which is a product of photosynthesis
And is when many glucose monomers join to make

Question 4

Why is starch favoured in a plant over glucose

Answer 4

Insoluble (won’t draw water into the cell through osmosis)
Compact (can fit a lot into the cell)
Broken down easily

Question 5

Give the formula of glucose and state what is made out of and where those elements come from

Answer 5

C6H12O6
Carbon and oxygen , comes from the carbon dioxide gas in the air
Hydrogen, comes from water

Question 6

Why can you not test in a school laboratory of water is a a factor for photosynthesis

Answer 6

Because if you deprived a plant of water it would wilt and die.

Question 7

How have scientists proved that plants need water for photosynthesis

Answer 7

By supplying the plant with labeled atoms such as a heavy isotopes of oxygen
And then observing if that isotope is present in the oxygen gas released from the plant

Question 8

Give the balanced chemical equation of photosynthesis

Answer 8

6CO2 + 6H2O ——) C6H12O6 + 6O2

Question 9

Describe the the energy transfer in the process of photosynthesis

Answer 9

Light energy is converted into chemical energy with the chlorophyll

Question 10

Explain how you could test that plants produce oxygen during photosynthesis

Answer 10

Place pondweed in a test tube of water under bright light
Count the number of bubbles produced in one minute to measure the rate of photosynthesis

Question 11

Explain how gas exchange occurs in the daylight in a leaf

Answer 11

So high concentration of co2 outside the leaf diffuses into the leaf which has low concentration of CO2
High concentration of oxygen in the leaf diffuses out to lower concentration of oxygen outside

(Bc in daylight leaf favors photosynthesis)

Question 12

Explain how gas exchange occurs in the night in a leaf

Answer 12

High concentration of CO2 inside diffuses out to lower conc of CO2 outside
High concentration of oxygen outside diffuses in to lower concentration of oxygen inside

Question 13

What two forms is starch transported in around the leaf and why not starch

Answer 13

Usually in the form of sucrose or amino acids, because they are soluble so can be converted into other compounds eventually but starch is not

Question 14

At what time of day is more CO2 given off and explain why
And at what time of day is more oxygen given off and explain why

Answer 14

More CO2 given off at night because respiration is higher than photosynthesis
More oxygen given off in the day because more photosynthesis than respiration

Question 15

Explain how to measure the affect of light intensity on gas exchange of a leaf

Answer 15

-Measure out 10cm^3 of hydrogen carbonate indicator into four test tubes
-Place a leaf inside three of the test tubes:
one leaf covered in aluminum,
One leaf covered in translucent material
One leaf without anything
-and leave the fourth test tube with no leaf in it to act as a control
-place all in bright light for a few hours and place rubber bung on them

-results:
aluminum leaf colour of solution; yellow bc no photosynthesis
translucent leaf colour of solution: orange bc rate of photosynthesis equal to rate of respiration
Leaf without anything colour of solution: purple bc photosynthesis high

Question 16

Three leaves are left in different test tubes in hydrogen carbonate solution.
One with aluminum on it
One with translucent material
One without any material.
Describe and explain the color changes

Answer 16

aluminum leaf colour of solution; yellow bc no photosynthesis (so co2 levels thus highest, as respiration is higher)
translucent leaf colour of solution: orange bc rate of photosynthesis equal to rate of respiration
Leaf without anything colour of solution: purple bc photosynthesis high (so oxygen given off is higher than co2)

Question 17

What is a limiting factor

Answer 17

Component of the reaction in shorted supply, which thus prevents the rate of reaction from increasing

Question 18

Give three examples of limiting factors on the rate of photosynthesis

Answer 18

1)carbon dioxide concentration
2)light intensity
3)temperature

Question 19

Give six ways in which leaves are adapted for gas exchange:

Answer 19

-thin, for short diffusion distance
-flat: for large surface area to volume ratio for maximum diffusion
-contain many stomata to maintain a high concentration gradient
-contain many internal air spaces for gases to move easily and to create a larger surface are to volume ratio for diffusion
-contain moist air to allow gases to dissolve for them to move easily
- close space between cells and air spaces for efficient gas exchange for photosynthesis and respiration

Question 20

Function of the waxy cuticle (2)

Answer 20

Prevents water loss by evaporation,
Acts as a barrier to prevent harmful disease carryingmicroorganisms from entering such as bacteria

Question 21

Function of upper epidermis:

Answer 21

Thin and translucent to allow light to enter into the palisade mesophyl

Question 22

Function of palisade mesophyl:

Answer 22

Contains many tightly compact column shaped cells
Contain many chloroplasts for maximum photosynthesis

Question 23

Function of spongy mesophyl

Answer 23

Main surface of gas exchange
And contains many air spaces to increase surface area to volume ratio for maximum diffusion

Question 24

Function of lower epidermis (3)

Answer 24

Contains guard cells and stomata
Where guard cells control when the stomata opens and closes
Stomata is where gas exchange takes place, and is also where evaporation of water occurs

Question 25

Function of stomata(2):

Answer 25

Where gas exchange takes place, allowing carbon dioxide to ENTER and oxygen TO LEAVE
Also where evaporation of water occurs

(Always talk abt stomata in terms of photosynthesis, bc at night you’re taught that they close, even tho technically a bit is still open to allow respiration to occur)

Question 26

Give the names of 7 products that glucose can become in a plant

Answer 26

Sucrose
Fructose
Starch
Cellulose
Lips
Proteins
Chlorophyll

Question 27

How is glucose converted into cellulose in a plant

Answer 27

When a plant photosynthesizes, glucose is produced
Plant then uses this glucose for aerobic respiration, which releases energy
The glucose from photosynthesis and energy from respiration are then used to make cellulose

Question 28

What is cellulose used for in a plant

Answer 28

Used to make the cell walls and to provide them with strength

Question 29

How does a plant make lipids, and what are these lipids used for

Answer 29

Makes them from glucose which is produced from photosynthesis.
They are used t9 make cell membranes of cells, and can be another energy store, stored on the seeds

Question 30

Explain how proteins can be made in a plant(4)

Answer 30

Plant photosynthesizes and glucose is produced.
This reacts with nitrate ions which are absorbed in the roots from the soil
And this produces amino acids
Many amino acids then join together to make a protein

Question 31

Explain how a plant can make chlorophyll

Answer 31

Plant photosynthesizes to produce glucose
This glucose then reacts with magnesium ions which are absorbed in the roots from the soil
To produce chlorophyll

Question 32

Give four minerals required for plants and their uses

Answer 32

Nitrates: used to make amino acids for proteins. And used for cell growth
Phosphates: used to make dna and cell membranes
Potassium: allow enzyme reactions to take place for respiration and photosynthesis
Magnesium: used to make chlorophyll

Question 33

Give the four deficiencies of the mineral ions needs for plants

Answer 33

Nitrate deficiency: old leaves turn yellow, and poor plant growth
Potassium deficiency: yellowed leaves with dead spots
Magnesium deficiency: yellowed leaves
Phosphate deficiency: young leaves begin to turn purple

Question 34

In a water culture experiment to investigate the effect of different deficiencies of minerals on a plant, explain why the conical flask in which the plant cutting is placed in is wrapped with aluminum foil

Answer 34

To prevent the growth of algae,
By preventing light from entering it so that it can not photosynthesize

Question 35

In a water culture experiment to investigate the effect of different deficiencies of minerals on a plant, explain why there is an aeration tube in the conical flask

Answer 35

To provide oxygen to the root hair cells
So that they can aerobically respire to produce energy for atp
Which can then be used for the process of active transport for mineral absorption

Question 36

Give two functions of lignification on the xylem

Answer 36

-makes the xylem strong so that it does not collapse when water is being transported up through it
-lignin is impermeable, so will not allow any water to be dissolved in the process

Question 37

Explain what would happen if the stomata were on the upper side of the leaf in terms of water loss

Answer 37

More sunlight would reach them, so there would be more evaporation of water through transportation
And more wind and air movement would reach them aswell, so thus more evaporation would occur

Question 38

Why do plants in drier conditions have less stomata on the underside

Answer 38

To reduce water loss by transpiration

Question 39

Explain how light intensity affects the rate of transpiration

Answer 39

-high light intensity means rate of transpiration increases
Because photosynthesis will occur, which means stomata will have to open
So more water vapour will diffuse and evaporate out

Question 40

Explain how temperature affects the rate of transpiration

Answer 40

High temperatures mean the rate of transpiration will increase
As water particles will have more energy
So will diffuse and evaporate out at higher rate

Question 41

Explain how air flow affects the rate of transpiration

Answer 41

Higher air flow/ wind means higher rate of transpiration
Bc the wind will remove any excess water vapour left on the leaf
Therfore the concentration gradient of the leaf will be maintained
And so water will diffuse at a higher rate

Question 42

Explain how humidity affects the rate of transpiration

Answer 42

The more humidity, means the rate of transpiration will be less
As there will be water vapour in the air aswell as in the leaf
So less concentration gradient between the air spaces and the external air for the water to diffuse
So less evaporation

Question 43

Explain the rate of transpiration in dry air

Answer 43

Rate of transpiration will be high
Because less water vapour will be in the air
So a high concentration gradient will be maintained between the internal air spaces and external side of the leaf
So more diffusion and thus more evaporation of water out of the leaf

Question 44

Explain how you can use a weight photometer to measure the rate of Transpiration

Answer 44

Place a plant on a scale and cover the soil with polystyrene bag to prevent the soil from evaporating
Then leave for a few hours and record the change in weight

Question 45

Give a critsicm of using a weight potometer to measure the change in transpiration

Answer 45

Mass may have decreased from the process of respiration or photosynthesis because these processes involve gas exchange, so we don’t know if all the mass lost was from transpiration

Question 46

Give two things you need to do when setting up a bubble potometer with a plant and why

Answer 46

1) cut the plant at an angle, and do this underwater so that no air can enter
2)dry the leaves and leave to acclimatize so that no excess water in them

Question 47

Explain the transportation stream

Answer 47

1)water evaporates inside the leaf to form water vapour
2)diffuses through the air spaces and out through the stomata because high concentration of water inside the life compared to outside the leaf
3)in response to this, the root hair cells absorb water and the xylem pulls it back into the leaf

Question 48

Give four functions of the transpiration stream

Answer 48

1)provides water for photosynthesis
2)provides a cooling effect for the leaf through the process of evaporation from the surface
3)transports mineral ions to the leaf by dissolving them in water
4) keeps the plant cells turgid, so keeps the plant supported

Question 49

Explain what happens to the guard cells in the light

Answer 49

Water moves into the guard cells by osmosis from a high concentration in the epidermis
To a low concentration in the guard cells
Thus become turgid
Which causes them to open

Question 50

Explain what happens to guard cells in the dark

Answer 50

Water moves out by osmosis from a high concentration in the guard cells
To a low concentration in epidermis
Therefore becoming flaccid
Which causes them to close

Question 51

Give two differences between a phloem cell and a xylem cell

Answer 51

Xylem cells are dead, phloem cells are alive
xylem cells water only moves upwards, phloem cells water can mov e upwards and downwards

Question 52

Explain how the structure of the xylem is formed

Answer 52

Begins like a normal cell with a cytoplasm and walls made of cellulose
Then eventually the cellulose wallah become lignin
This causes the cell to die
And thus a hollow tube is created

( so basically talking about it in terms of lignin and hollowness)

Question 53

Give the function of the xylem

Answer 53

To transport water and minerals up the root through the stem and into the leaf

Question 54

Give the function of the phloem

Answer 54

Transports substances such as sucrose and amino acids
made from photosynthesis
To other parts of the plant where they are requird

Question 55

Which two tissues are in the vascular bundle

Answer 55

The xylem and the phloem

Question 56

What is transpiration

Answer 56

The loss of water from a plant by evaporation

Question 57

How do plants take in water

Answer 57

The root hair cells absorb water by osmosis
Because water moves from a high water potential in the soil to a low water
Across a partially permeable membrane

Question 58

Explain how plants uptake minerals

Answer 58

Plants uptake minerals by the process of active transport in the root hair cells
Where because the mineral concentration is higher in the cell than in the soil,
They move against a concentration gradient using ATP

Question 59

When testing a leaf for starch why is it boiled in hot water forst

Answer 59

To kill the leaf and stop chemical reactions from happening

(Remember that the waxy cuticle aswell stops water from entering the plant)

Question 60

When testing a leaf for starch why is it boiled in ethanol

Answer 60

To remove the chlorophyll, so that it is colored and you can easily see the colour change when iodine is added

Question 61

Explain how very high temperatures could reduce the growth of a plant (3)

Answer 61

-it would decrease the rate of of photosynthesis
-because the enzymes would be denatured so change in active site shape so less enzyme substrate collisions

-thus less CO2 would be taken in

-it would also mean more transpiration would occur
-this means that the plant will lose its turgid and begin to wilt

Question 62

Explain why when measuring the affect of the colour of light on photosynthesis, plant that used blue light had a higher rate of photosynthesis than the plant that used green light

Answer 62

Blue light was absorbed
Green light was reflected (bc same colour as chlorophyll)

Question 63

A student carries out an experiment to investigate the effect of changing the colour of light on the rate of photosynthesis in a water plant.
Explain and suggest how the student can control 4 variables

Answer 63

1)carbon dioxide; add same mass of hydrogen carbonate indicator to see how much co2 present
2)Light intensity: distance from lamp
3)mass / surface area of plant / number of leaves / species /
same plant
4) temperature, using a water bath and thermometer

Question 64

Give two reasons why plants do not absorb all of the energy from the sun

Answer 64

Because they do not absorb all wavelengths, some are reflected
Not all the light falls onto the leaves which contain the chlorophyll , eg some falls onto the flowers