Plant Structures And Their Functions Flashcards
Describe the structure of the xylem
- 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
Describe the structure of the phloem
- 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
Describe the process of transpiration
- 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
How do stomata open and close?
- 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
Describe the process of translocation
- 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
How does light intensity affect transpiration?
- 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
How does air movement affect transpiration?
- 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
How does temperature affect transpiration?
- The higher the temperature the more energy the water molecules have
- This means they move faster which means a faster rate of transpiration
How do you use a potometer to measure the rate of transpiration?
- 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

What is a tropism?
A plant’s response to a stimulus by growing
Describe the function of auxins in growing shoots
- 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
Describe the function of auxins in growing roots
- 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
How are auxins used in selective weed killers?
- 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
What is rooting powder used for?
- 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
What are gibberellins and what are they used for?
- 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
How does ethene cause fruits to ripen?
- Ethene is a hydrocarbon gas so it speeds up ripening in fruit
- Fruits also release ethene naturally
What is the equation for photosynthesis?
Carbon dioxide + Water >
Glucose + Oxygen
What is a limiting factor?
A factor which, if in short supply, limits or reduces the rate of photosynthesis
How are the rate of photosynthesis and light intensity/CO2 concentration related?
They are directly proportional until another factor becomes limiting
How are the rate of photosynthesis and temperature related?
As temperature increases, the rate of photosynthesis increases
However at high temperatures, enzymes are denatured which will decrease the rate of photosynthesis
How do you investigate how light intensity affects the rate of photosynthesis?
- Place 20 algae balls and the same volume of indicator solution in each screwtop bottle
- Check colour of indicator against colour chart and record starting pH
- If using a hot lamp, place water tank next to lamp
- Use a meter ruler to place the bottles at specific distances from the lamp
- Leave the bottles for 1-2 hours
- Record distance and pH of each tube, using the colour chart for pH
What are the different adaptations of a leaf (the parts)?
Waxy cuticle
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Airspace
Lower epidermis
Guard cells
What is the purpose of the waxy cuticle?
- Transparent to let light through
- Protect the leaf from infection
- Prevent water loss
What is the purpose of the upper epidermis?
- Transparent collect light through to palisade cells
How is the palisade mesophyll adapted to its function?
- Flattened shape gives large surface area
- Packed with chloroplasts for photosynthesis
What is the purpose of the airspace’s in the spongy mesophyll?
- Allow carbon dioxide to diffuse through the leaf
How are plants adapted to dry conditions?
- Waxy cuticle to reduce water loss
- Leaf hairs to trap moist air around stomata
- Rolled leaf to reduce air movement around stomata
- Stomata sunk in pits to reduce water loss
How are plants adapted to tropical conditions?
- Large leaves to take in as much light as possible
- Stems and leaves that climb up the trees to obtain more light
- Leaves with ‘drip tips’ so water runs often
How are plants adapted to waterlogged soil?
- Spongy tissue in their roots that stores oxygen
- Fine surface roots that take in oxygen at the water surface
