topic 6 - plant structures and their functions

Question 1

describe photosynthesis

Answer 1

• occurs in plants and algae.
• an endothermic reaction, so it takes in more energy than it releases.
• Light energy from the environment is transferred to chloroplasts in leaves.
  carbon dioxide + water -> glucose + oxygen
  six CO2 + six H2O –> C6H12O6 + six O2

Question 2

How temp. affects rate of photosynthesis

Answer 2

• increase in temp. – the rate of
  photosynthesis increases.
• reaction is controlled by enzymes, so the rate increases up to a certain temperature
• then enzymes begin to denature and the rate of the
  reaction decreases

Question 3

How light intensity affects rate of photosynthesis

Answer 3

• For most plants, the higher the light
  intensity, the faster the rate of the
  reaction.

Question 4

How CO2 conc. affects rate of photosynthesis

Answer 4

• Carbon dioxide is needed to make
  glucose
• As the conc. of carbon dioxide increases,
  the rate of reaction increases.

Question 5

Describe limiting factors in photosynthesis

Answer 5

• an environmental condition e.g. light intensity which, in low levels, restricts any increase in the rate of
  photosynthesis.
• even if other factors increase e.g. temp. or CO2 conc. the rate of photosynthesis will not increase any more.
• can be seen on a graph as the curve levelling off.

Question 6

How to measure the oxygen production of a plant

CoRe pRAcTICaL

Answer 6

• Pondweed is placed in a test tube full w/ water. top is sealed
• capillary tube also containing water, leads into the test tube, and it’s attached to a syringe.
  ● lamp is placed at a measured distance from test tube.
  ● As it photosynthesises, oxygen is produced, forming a gas tube in the capillary tube
  ● distance the bubble has moved is measured using a ruler to calculate vol. of oxygen produced.
  ● Many variables can be changed to observe their effect on photosynthesis: the temp. (using a water bath), time the pondweed is left, the light intensity (varied
  by the distance the lamp is from the plant).
  ● important to control all factors that may affect photosynthesis except your
  independent variable (the one you want to observe), so it is a valid experiment.

Question 7

describe limiting factor graphs

Answer 7

• A graph involves one limiting factor if it has one line which levels off,
• rate of photosynthesis is on the vertical axis.
• A graph w/ two lines represents two limiting factors in two experiments.
• investigation is carried out at two different environmental conditions e.g. two different temperatures

Question 8

Why is light intensity directly proportional to the rate of photosynthesis

Answer 8

• because the greater the intensity of light, the more photons (light energy) that hit the chloroplasts in the leaf, and the more photosynthesis can occur
  at once.

Question 9

Describe inverse square law

Answer 9

• As the distance between the light source and the plant increases, the light intensity decreases.
• light intensity is inversely proportional to the square of the distance- called the inverse square law.

Question 10

How are root hair cells specialised?

Answer 10

• specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots
• Have a large surface area due to root hairs, meaning more water can move in
• The large permanent vacuole affects the speed of movement of water from the soil to the cell
• Mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell

Question 11

How are xylem cells specialised

Answer 11

• specialised to transport water and mineral ions up the plant from the roots to the shoots
• chemical called lignin is deposited which causes the cells to die. Cells become hollow and are joined end-to-end to form a continuous tube so water and
  mineral ions can move through.
• Lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water

Question 12

How are phloem cells specialised

Answer 12

• specialised to carry the products of photosynthesis to all parts of the plants
• Cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell
• cells within phloem are alive
• Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells.
• cells use this energy to transport sucrose around the plant

Question 13

What is transpiration ?

Answer 13

• the loss of water of water vapour from the leaves and stems of the plant
• It is a consequence of gaseous exchange, as the stomata are open so that this can occur.

Question 14

Describe transpiration

Answer 14

• Water evaporates at the open stomata (pores) on the leaf surfaces
• As water molecules are attracted to each other, when some molecules leave the plant the rest are pulled up through the xylem
• so more water being taken up from the soil resulting in a continuous transpiration stream through the plant

Question 15

Describe guard cells and how they control the stomata

Answer 15

• They close and open stomata and are kidney shaped
• They have thin outer walls and thick inner walls
• When lots of water is available to the plant, the cells fill and change shape, opening stomata (they are also light sensitive)
• This allows gases to be exchanged and more water to leave the plant via evaporation
• More stomata are found on the bottom of the leaf, allowing gases to be exchanged whilst minimising water loss by evaporation since the lower surface is shaded and cooler.

Question 16

What is translocation

Answer 16

-it’s the movement of food substances (such as sucrose) made in the leaves, up or down the phloem, for immediate usage or storage.

Question 17

Describe translocation

Answer 17

• it only occurs in the phloem
• Translocation of sucrose occurs from the sources to
  the sinks (the places where it used or stored)
• The location of the sources and sinks can depend on the season. e.g. in spring the source could be located in the root, and the sink in the leaf - and in summer this could be the other way around.

Question 18

How is a stomata adapted for its function

Answer 18

• They’re able to close to minimise water loss and open to increase evaporation and transpiration.
  -they also allow gas exchange to occur when they are
  open.

Question 19

How is chlorophyll adapted to its function

Answer 19

• Chlorophyll is green, which is the most efficient colour for absorbing light. This means that the most light possible is absorbed

Question 20

How is the thinness of the leaf adapted to its function

Answer 20

• Leaves are very thin, so carbon dioxide only has a short distance to travel to enter the leaf and oxygen only has a short distance to diffuse out

Question 21

How is the large surface area of the leaf adapted to its function

Answer 21

• a large surface area means that the leaf can absorb more light at once, maximising the rate of photosynthesis

Question 22

How does an increase in temp. affect the rate transpiration

Answer 22

• molecules move faster, so evaporation
  happens at a faster rate and so the rate of
  transpiration increases.
• The rate of photosynthesis increases, so more stomata are open for gaseous exchange, so more water evaporates and the rate of transpiration increases.

Question 23

How does an increase in humidity affect the rate of transpiration

Answer 23

• If the relative humidity is high, then there will be a reduced concentration gradient between the concentrations of water vapour inside and outside the leaf, so there’s a slower rate of diffusion. This will decrease the rate of transpiration

Question 24

Hows does increased air movement (wind) affect the rate of transpiration

Answer 24

• more air is moving away from the leaf, so the concentration of water vapour surrounding the
  leaf will be lower.
• So there will be a steeper concentration gradient resulting in diffusion happening faster.
  This increases the rate of transpiration.

Question 25

How does increased light intensity affect the rate of transpiration

Answer 25

• it leads to an increased rate of photosynthesis, so more stomata open to allow gaseous exchange to occur.
• so more water can evaporate, leading to an increased rate of transpiration

Question 26

What do you use to calculate the rate of transpiration

Answer 26

• a potometer

Question 27

How do you calculate the rate of transpiration

experiment

Answer 27

• by using a potometer, it involves placing a plant in a capillary tube in water, and measuring the distance travelled by a bubble.
• place a leaf shoot in one end of the potometer, and use a ruler to measure how far the bubble travels up the capillary tube in a set time
• further the bubble moves in this time, the greater the rate of transpiration

Question 28

Why do we measure the water uptake when trying to calculate the rate of transpiration

Answer 28

• Measuring the uptake of water by the plant gives an indication to the rate of transpiration, because water is only taken up if water leaves the plant

Question 29

Why do some plants have extreme adaptations

Answer 29

• Many plants are adapted to survive in extreme environments. To do so, they need to have
  specific adaptations which maximise their ability to take in sunlight and carbon dioxide

Question 30

How has the leaf shape and size adapted (extreme adaptations)

Answer 30

• many desert plants do not have leaves, or have very small leaves.
• so this reduces the amount of water lost as a result of transpiration.

Question 31

How has the waxy cuticle adapted (extreme adaptations)

Answer 31

• they have a waxy cuticle on top, preventing

evaporation of water in environments where water is scarce.

Question 32

How has the stomata adapted (extreme adaptations)

Answer 32

• they’re small pores on the surface of a leaf.
• They can be closed to prevent evaporation of water in extreme environments, and opened when carbon dioxide is needed for photosynthesis.
• so the plant can adapt when water is scarce.

Question 33

What are hormones in the plant used for

Answer 33

• they are used to coordinate and control growth

Question 34

Differences between :
Phototropism
Gravitropism/ Geotropism

Answer 34

phototropism- the response to light

gravitropism/ geotropism- the response to gravity

Question 35

How does auxin control the plant

Answer 35

• it moves to the shaded side of the shoot and the auxin stimulates cells to grow more here. plants show positive phototropism because they grow towards the light source.
• plant is exposed to light on one side so the shoot bends towards the light.
• plant receives more light, so photosynthesis can occur at a faster rate

Question 36

What is auxin

Answer 36

• a plant hormone which causes the elongation of cells in shoots and is involved in regulating plant growth.
  ● the shoot bends towards the light.
  ● The plant receives more light, meaning photosynthesis can occur at a faster rate.

Question 37

What is negative gravitropism

Answer 37

• they grow away from gravity.
  ● Auxin moves to the lower side.
  ● The cells of the shoot grow more on the side with most auxin, so it stimulates cells to grow more here.
  ● the shoot bends and grows away from the ground.

Question 38

Why can negative gravitropism be beneficial

Answer 38

● This is beneficial as light levels are likely to be higher the further away they are from the ground.

Question 39

What is positive phototropism

Answer 39

• they grow towards gravity. If a root is horizontal:
  ● Auxin moves to the lower side.
  ● The cells of the root grow more on the side with less auxin, so it stimulates cells to grow on the upper side.
  ● This makes the root bend and grow downwards.

Question 40

Why can positive phototropism be beneficial

Answer 40

● This is beneficial as there are more likely to be increased levels of water and nutrients lower down, and it provides stability for the plant.

Question 41

What happens when the auxin distribution is equal

Answer 41

When the auxin distribution is equal on both sides it grows straight in that direction.