Plant Structures And Their Functions Flashcards
1
Q
Describe the structure of the xylem
A
- Dead cells which have no cytoplasm or organelles, this means more space for water to move through
- Holes called pits in their walls to allow water and mineral ions to move out
- Lignified cells are strong and prevent collapsing
- No end walls so water can flow through easily
2
Q
Describe the structure of the phloem
A
- Contains sieve tube elements have no nucleus and very little cytoplasm so there’s lots of space to transport sucrose
- Also contains companion cells which have lots of mitochondria to produce energy for active transport of sucrose in and out of the sieve cells
3
Q
Describe the process of transpiration
A
- Water enters roots by osmosis
- Draws water up the stem through the xylem from roots
- Draws water out of the leaf cells and xylem
- Water vapour evaporates from leaves mainly through the stomata
4
Q
How do stomata open and close?
A
- When guard cells take in water by osmosis, they swell which causes the stoma to open
- When guard cells lose water, they become flaccid and the stoma closes
5
Q
Describe the process of translocation
A
- Sucrose is produced in leaves from glucose formed in photosynthesis
- Dissolved sucrose is carried around the plant in the phloem
- Dissolved sucrose is used for growth in growing regions such as buds
- Dissolved sugars are converted to starch and stored in storage organs (such as potatoes) to be used later
6
Q
How does light intensity affect transpiration?
A
- High light intensity causes the stomata to open
- This increases the rate of evaporation of water from the leaf
- This means more water is taken up to replace this
7
Q
How does air movement affect transpiration?
A
- Wind blows moist air away from the stomata
- This keeps the diffusion gradient high
- The more air movement there is the higher the transpiration rate
8
Q
How does temperature affect transpiration?
A
- The higher the temperature the more energy the water molecules have
- This means they move faster which means a faster rate of transpiration
9
Q
How do you use a potometer to measure the rate of transpiration?
A
- Record the position of the air bubble on the ruler at the start
- Record the position of the bubble on the ruler after a known number of minutes
- Divide the distance moved by the bubble by the time taken, this gives you the rate of transpiration

10
Q
What is a tropism?
A
A plant’s response to a stimulus by growing
11
Q
Describe the function of auxins in growing shoots
A
- Auxins are produced in cells near the top of the shoot
- They move to the shaded part of a shoot
- They cause elongation so the plant bends towards the light
12
Q
Describe the function of auxins in growing roots
A
- A high concentration of auxin in roots inhibits cell elongation
- There is a higher concentration of auxins and the bottom side of a root
- This means that cells on the other side of the route elongate more causing the root to bend down
13
Q
How are auxins used in selective weed killers?
A
- Selective weedkillers contain growth hormones that cause the weeds to grow too quickly and die
- The weeds have broader leaves so the weedkiller is absorbed in larger quantities than the plant
14
Q
What is rooting powder used for?
A
- It contains auxins to promote growth
- Plant cuttings can be dipped in rooting powder before planting
- This helps cuttings to grow quickly into fully developed plants
15
Q
What are gibberellins and what are they used for?
A
- Stimulates germination of seeds which increases crop yields
- Stimulate stem elongation so plants grow taller
- Promote flowering which results in more financially profitable flowers
- Used in the production of seedless fruit
