Plant Structures and Their Functions

Question 1

How is the xylem tissue adapted to its functions?

Answer 1

• Made up of hollow cells designed to carry water
• made up of dead cells joined end to end with no end walls and a hole down the middle
• strengthened by lignin
• Thick, strengthened cellulose cell wall

Question 2

How is phloem issue adapted to its function?

Answer 2

• Columns of elongated living cells
• Companion cells contains lots of mitochondria which store energy needed for active transport
• Small pores in end walls to allow rapid transport of food substances through sieve tubes

Question 3

Describe how transpiration occurs

Answer 3

• caused by the evaporation and diffusion of water from a plants surface (in leaves)
• The loss of water creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels
• This causes a constant transpiration stream of water through the plant

Question 4

Describe how translocation occurs

Answer 4

The phloem transports food substances (e.g. sucrose) made in the leaves to the rest of the plant for immediate use (growing regions) or for storage. This process needs energy from respiration and goes in both directions

Question 5

How does light intensity affect transpiration rates?

Answer 5

• The brighter the light, the greater the transpiration rate

- Stomata close when dark so little water can escape

Question 6

How does light intensity affect transpiration rates?

Answer 6

The brighter the light, the greater the transpiration rate because stomata close as it gets darker as photosynthesis cannot happen (so CO2 doesn’t need to be let in) and so less water can escape

Question 7

How does temperature affect transpiration rates?

Answer 7

The warmer, the faster transpiration happens
(because water particles have more energy to evaporate and diffuse out the stomata)
( - reaches optimal temp and enzymes begin to denature, slowing photosynthesis )

Question 8

How does air flow affect transpiration rates?

Answer 8

The more air flow, the greater the transpiration rate - a poor air flow means the water vapour surrounds the leaf and doesn’t move away - a good air flow means water vapour is in low concentration so diffusion is quicker

Question 9

How does humidity affect the rate of transpiration?

Answer 9

The more humid the smaller the rate of transpiration - more water particles in air means that diffusion will happen more slowly (high to not as low concentration)

Question 10

How can the rate of transpiration be measured?

Answer 10

Using a potometer - measures water uptake by a plant but assumes water uptake is linked to water loss - air bubble moves along a tube towards a plant - calculate speed of bubble

Question 11

Using a potometer, how can transpiration rate be obtained?

Answer 11

Rate of transpiration = Distance moved (by bubble) / Time taken (for bubble to move)

Question 12

How are root hair cells adapted to take in water and minerals?

Answer 12

Cells on the surface of a root are covered in millions of hairs - Large surface area for absorbing as much water as possible
Thin cell walls so can absorb water easily

Question 13

What is diffusion?

Answer 13

The net movement of particles from an area of high concentration to an area of low concentration. Movement is random and passive

Question 14

What is osmosis?

Answer 14

He movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane. Movement is random and passive

Question 15

What is active transport?

Answer 15

The movement of substances from a low to high concentration against the concentration gradient. Requires energy

Question 16

What is the concentration gradient?

Answer 16

The difference in concentration between two areas

Question 17

How can diffusion be sped up?

Answer 17

• Distance - the shorter distance particles need to move
• Concentration gradient - the greater the difference in concentration
• Surface area - the greater the surface area the particles must diffuse across

Question 18

What does hypotonic mean?

Answer 18

Low concentration of water particles (compared to potato)

Question 19

What does isotonic mean?

Answer 19

Same amount of particles in the potato and the solute

Question 20

What does hypertonic mean?

Answer 20

Higher concentration of particles

Question 21

What does turgid mean?

Answer 21

Lots of water in a plant cell (less concentrated solute)

Question 22

What does flaccid mean?

Answer 22

Less water in a plant cell (more concentrated solute)

Question 23

What is Lysis?

Answer 23

When animal cells burst from too much water

Question 24

What is cremation?

Answer 24

Animal cell without much water

Question 25

How can you investigate osmosis?

Answer 25

• Prepare sucrose solutions of varying concentrations (pure water to very concentrated)
• Cut a potato into same sized pieces (about 1cm in diameter)
• Use a mass to measure the mass of each cube and place one in each solution for 40 mins (could use groups of potatoes rather than single ones for more accuracy)
• Remove potatoes and dry gently (removing excess water) and weigh each potato and record your results

Question 26

What is an endothermic reaction?

Answer 26

The products of the reaction contain more energy than the reactants (energy taken in)

Question 27

What is an exothermic reaction?

Answer 27

The reactants of the reaction contain more energy than the products (energy produced)

Question 28

What is meant by biomass?

Answer 28

The mass of living material

Question 29

How are photosynthetic organisms producers of biomass?

Answer 29

Photosynthesis uses energy from the sun to create glucose which is used to make larger, complex molecules that the plants need to grow - making up the organism’s biomass - this energy stored in the organisms biomass then makes its way through the food chain as animals eat the plant and each other

Question 30

What is the word equation for photosynthesis?

Answer 30

Carbon Dioxide + Water -> Glucose + Oxygen

Question 31

How are leaves adapted for photosynthesis?

Answer 31

• Contain chloroplasts which contain Chlorophyll which absorbs light energy (palisade cells)

Question 32

What is the name of the law which calculates light intensity?

Answer 32

Inverse square law

Question 33

What is the inverse square law?

Answer 33

light intensity = 1

d²

Question 34

What is the compensation point?

Answer 34

Rate of photosynthesis equals the rate of respiration

Question 35

How is CO2 concentration a limiting factor of photosynthesis rate?

Answer 35

• more increases the rate of photosynthesis - more CO2 to make sugars
• once CO2 concentration is high, photosynthesis become the limiting factor as CO2 has reached an optimal level

Question 36

How is temperature a limiting factor of photosynthesis rate?

Answer 36

• hotter temp increases kinetic energy of molecules and enzyme activity so photosynthesis speeds up
• if the temp is too high enzymes will denature and photosynthesis slows down as the optimal level has been passed

Question 37

What kind of reaction is photosynthesis?

Answer 37

endothermic - energy is taken in during the reaction

Question 38

How can you investigate the effect of light intensity on the rate of photosynthesis?

Answer 38

1. set up a conical flask filled with Canadian pondweed and water, attach a gas syringe to the top of the conical flask
2. Sodium hydrocarbonate may be added to the water to make sure the plant has enough CO2
3. a light source is placed at a specific distance from the pondweed (measured with a ruler)
4. pondweed is left to photosynthesise for a set time - oxygen will collect in the gas syringe so you can measure the volume of oxygen produced
5. experiment repeated with light source at varying distances (rate of oxygen produced is calculated - volume produced divided by time taken)
6. control variables: temp controlled by putting the conical flask in a water bath - CO2 concentration controlled by adding set amount of sodium hydrocarbonate to set volume of water

Question 39

How is light intensity a limiting factor of photosynthesis?

Answer 39

• light transfers the energy needed in photosynthesis so as the light level is raised the rate of photosynthesis increases steadily
• beyond that, light won’t make any difference and temperature or CO2 will be the limiting factor

Question 40

What do root hair cells do and how are they adapted to do this?

Answer 40

• each root is covered in millions of hair cells - giving the plant a large surface area for absorbing water and mineral ions from the soil - concentration of mineral ions is greater in the root hair hair cell than the soil around it so the ions are absorbed by active transport

Question 41

What are stomata?

Answer 41

tiny pores on the surface of a plant - mostly found on the lower surface of leaves - allow gas exchange and water vapour to escape through diffusion - surrounded by guard cells which change shape to control the size of the pore (open when turgid and close when flaccid)

Question 42

Why do stomata close when dark?

Answer 42

Because photosynthesis can’t happen without light energy, so they don’t need to be open to let in CO2 - this means little water can escape