SB6 - Plant Structures and their Functions ✓

Question 1

SB6a - How are leaves adapted for their purpose?

Answer 1

• Broad and Flat - Large surface area to trap more energy
• Palisade Cells - These are packed with chloroplasts to trap sunlight energy
• Leaf Stomata - Microscopic pores allow for gas exchange
• Guard Cells - Controls the Opening/Closing of the Stomata
• Thin Cells - Reduces diffusion pathway for gas exchange
• Spongy Mesophyll Tissue - Contains air spaces which increase the rate of gas exchange

Question 2

SB6a - What does photosynthesis do?

Answer 2

It traps energy from the sunlight and converts it to glucose

Question 3

SB6a - What is a plant’s biomass?

What are producers in a food chain?

Answer 3

The materials in an organism

Organisms that produce their own biomass and the produce the food for almost all other life on earth (PLANT AND ALGAE)

Question 4

SB6a - What is the equation for photosynthesis?

Answer 4

Carbon dioxide + Water → Glucose + Oxygen

Question 5

SB6a - What is the equation for respiration?

Answer 5

Glucose + Oxygen → Carbon dioxide + Water

Question 6

SB6a - What type of reaction is photosynthesis?

Answer 6

• Endothermic.
• The products have more energy than the reactants.
• This means they have taken in energy from the surroundings during the reactions

Question 7

SB6a - Where does photosynthesis occur?

Answer 7

In the chloroplasts of the plant cell

Question 8

SB6a - Why are the stomata an example of a gas exchange system?

Answer 8

They let carbon dioxide diffuse in and let oxygen diffuse out

Question 9

SB6a - Why is glucose necessary?

Answer 9

• Glucose molecules are joined together to form a polymer of starch.
• After photosynthesis stops, this is broken down to simple molecules which are used to form sucrose.
• Sucrose is used to make:
  
  • Starch (In a storage organ such as a potato)
  • other molecules for the plant (cellulose, lipids etc.)
  • Glucose for respiration (to release energy)

Question 10

SB6b - A graph showing how increasing rate of light intensity affects rate of photosynthesis eventually levels out. Why can’t it get any higher despite light intensity increasing?

Answer 10

• As the graph curves, light intensity is the limiting factor.
• Once it levels out, something else is the limiting factor.

Question 11

SB6b - Once the rate of photosynthesis can’t increase anymore (due to light intensity in this case) how would you increase the rate of photosynthesis?

Answer 11

• Something else is the limiting factor.
• Increasing the CO2 concentration or increasing the temperature will allow the rate of photosynthesis to continue to increase.
• Eventually it will level out again as something else has become the limiting factor.

Question 12

SB6b - What are the three main limiting factors that affect photosynthesis?

Answer 12

• Carbon dioxide concentration
• Light Intensity
• Temperature

Question 13

SB6b - What is the inverse square law, and where does it apply to?

Answer 13

• The inverse square law is used to find out how light intensity changes with distance from the source.
• I: light intensity
• d: distance

l (new) = l orig x d^2 (orig) / d^2 new

light intensity is inversely proportionate to the square of the distance

Question 14

SB6b - Why are plants less likely to grow higher up on a mountain?

Answer 14

Higher up, the air pressure is lower meaning the carbon dioxide concentration is lower

Question 15

SB6b - Why is it that even if temperature is the limiting factor, you’ll get to a point where increasing it won’t increase the rate of photosynthesis?

Answer 15

• At a temperature that is too high, the enzymes in the plant become denatured.
• They can no longer bind to their substrate and therefore processes can’t occur anymore

Question 16

SB6b CP - Describe a method, using algae balls and hydrogen carbonate indicator, to investigate rates of photosynthesis at differing light intensities.

Answer 16

1. Add 20 algae balls and the same amount of indicator to as many glass bottles as you need
2. Compare the colour of the bottle at the start to a key to work out its starting pH (they should all be the same)
3. Place a tank of water between the light and the first glass to absorb the heat given off by the light
4. Cover one with foil so it is in the dark and place it next to the one closest to the lamp
5. Measure out the distances you place all of the bottles
6. Turn on the light and wait till you see noticable changes in the pH
7. Once you’ve decided to stop, work out the pH again by comparing to a key
8. Work out the change in pH/hour to be your rate of reaction
9. Plot a graph of rate of reaction vs distance from light

Question 17

SB6c - How are roots adapted to absorb water?

Answer 17

• Roots have root hair cells
• The hairs make the surface area larger meaning there is more area for mineral ions to be quickly absorbed through water

Question 18

SB6c - How can some water enter the root hair cells if not through openings?

Answer 18

• The root hair cells have a semi-permeable membrane meaning that osmosis can take place with the water moving down the concentration gradient into the cytoplasm of the cell

Question 19

SB6c - How do plants take in mineral ions?

Answer 19

• Through the water they absorb.
• However as there is a higher concentration of these in the plant than in the soil, they can’t absorb it through diffusion but rather through active transport which takes up energy

Question 20

SB6c - What do root hair cells and root cells have between them and why?

Answer 20

They have a little tube allowing diffusion of fluids between cells

Question 21

SB6c - What is a concentration gradient and what can it cause to occur?

Answer 21

• When two areas are connected in some way and having differing levels of concentration of a substance, they have a concentration gradient
• If this is in a fluid, diffusion can occur, where the substance moves from the area of higher to lower concentration

Question 22

SB6c - What are the 4 uses of water in plants?

Answer 22

To be used in/to:

• Carrying dissolved mineral ions
• Keeping cells rigid so plants don’t wilt (droop)
• Cooling leaves (when it evapourates)
• Photosynthesis

Question 23

SB6d - Describe how you can investigate rates of transpiration

Answer 23

• A potometer is used for this. It involves using a plant attached to a rubber stopper connected to a reservoir of water and a capillary tube.
• The capillary tube should have at least one bubble in it and should have a scale .
• As the plant uses up water it will draw water from the tube moving the air bubble.
• The speed of the bubble will allow you to calculate the rate of transpiration

Question 24

SB6d - Describe the adaptations of the phloem

Answer 24

• No nucleus or cytoplasm as they aren’t needed and would be a waste of energy. They create more room for the central channel
• Companion cells to pump have many mitochondria so they have energy to actively transport sucrose
• Pore through whcih sucrose solution can be pumped

Question 25

SB6d - Describe the adaptations of the xylem

Answer 25

* Found in the plant stem, form **long tubes.** These tubes carry water and other dissolved minerals * Thick cellulose cell walls strengthened by lignin prevents it from bursting due tot eh water pressure. * Lignin kills the xylem cells, this ensures no water is used up in cell processes. * End walls are also broken to create one long tube, so water flow isn't impeded. * Xylem cells have no subcellular structures e.g cytoplasm, nucleus, vacuole or chlorplasts so the path of water isn't obstructed.

Question 26

SB6d - Describe the factors that affect transpiration.

Answer 26

* **Light intensity**: stomata opens wider allowing water in quicker * **Temperature**: More evapouration means a greater concentration gradient on the leaf surface * **Wind speed**: Less water on leaf surface steepens the concentration gradient, increasing rate * **Low humidity**: As the air becomes less saturated, water vapour evaporates more easily steepening the concentration gradient, increasing rate

Question 27

SB6d - Describe the process of translocation

Answer 27

* Translocation is the **movement** of **food substances** (such as sucrose) made in the leaves up or down the phloem, for use immediately or storage. * Plants make sucrose from glucose and starch made by photosynthesis. It is then **translocated** in the **sieve tubes** of the **phloem tissue**. The large central channel in each sieve cell is connected to its neighbours by **pores**, through with sucrose solution flows. * Companion cells **actively pump** sucrose into or out of the seive cells that form the sieve tubes. As sucrose is **pumped into sieve tubes**, the **increased pressure causes the sucrose solution to flow up to the growing shoots or down to storage organs.**

Question 28

SB6d - Describe the process of transpiration

Answer 28

Transpiration is the loss 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. ● Water also **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 ● This results in more water being taken up from the soil resulting in a continuous transpiration stream through the plant

Question 29

SB6e - How do plants reduce water loss?

Answer 29

* Having stomata located inside small pits - where water vapour collects because it is less exposed to air movement * By losing leaves in winter (deciduous), preventing water loss when soil water may be frozen * By opening stomata at night, CO2 is taken i nat night and stored for use during the day.

Question 30

SB6e - Describe how specialised guard cells open/close stomata

Answer 30

* 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 as the lower surface is shaded and cooler.

Question 31

SB6e - What are the 2 structural adaptations plants have for photosynthesis?

Answer 31

* Epidermis cells are **transparent**, allowing light to pass through the easily * They also produce a **waxy cuticle** which helps to prevent water loss

Question 32

SB6e - Why do some plant have needle shaped leaves?

Answer 32

* Small leaves result in a reduced surface area so transpiration happens more slowly. * A thick cuticle protects them from infection. * The smaller leaves helps them to withstand strong winds and a lack of water

Question 33

SB6f - Describe Darwin's experiments with auxin and what can be concluded from the results.

Answer 33

* Three intact shoots exposed to light. One covered with a black cap, one with a transparent cap and one normal * The one with the black cap didn't bend towards the light while the other two did * This shows that auxins are dependent on light to work * One where the tip was removed didn't bend towards the light. * This showed that auxins are produced in the tip of the shoot

Question 34

SB6f - How does gravitropism occur?

Answer 34

* Auxins in the root are pulled down by gravity. * They inhibit cell elongation here causing the root to grow downward

Question 35

SB6f - How does phototropism occur?

Answer 35

* Auxins are produced at the very tip of the shoot and move down the shoot * As auxins move downwards, they move to the shaded parts of the shoot. * This makes the cells elongate on the shaded side so the shoot bends towards the light

Question 36

SB6f - What are positive and negative phototropism and gravitropism?

Answer 36

* Positive = towards * Negative = away * Phototropism = a response to light * Gravitropism = a response to gravity

Question 37

SB6f - What are the names of three main plant hormones?

Answer 37

* Auxins: promote growth * Gibberellins: cause germination * Ethene: cause fruit ripening

Question 38

SB6g - How are auxins used by plant growers?

Answer 38

* **Selective weedkillers** contain artificial auxins to **kill plants** with broad leaves as they grow uncontrollably * Auxins are also used in **rooting powders** which cause **plant cuttings** to grow **roots** rather quickly

Question 39

SB6g - How is ethene gas used commerically?

Answer 39

As ethene controls ripening, it is used in the food industry. ● Fruit is picked when it is not ripe ● It is firm which means that during transport it gets less bruised and damaged ● When it is needed to be sold, it is exposed to ethene and warmer temperatures ● Ethene is involved in controlling cell division and stimulates enzymes that result in fruit ripening . ● This reduces wastage as more fruit is suitable to be sold and it does not ripen too early

Question 40

SB6g - What are the uses of gibberellins?

Answer 40

* Produce seedless fruits * Promote flowering * Increase fruit size * Germinate seeds