B6 - Plant Structures and Their Functions Flashcards
What is the equation for
photosynthesis?
carbon dioxide + water -> glucose + oxygen
6CO2 + 6H2O -> C6H12O6 + 602
this process requires light and chlorphyll
What factors affect
photosynthesis?
(3)
- light intensity
- concentration of CO2
- temperature
What are phloem tubes made of?
columns of elongated living cells with small pores in the end walls to allow stuff to flow through
What are some key points about
translocation?
(4)
what?
from where to where?
any requirements?
what direction?
- it is the transportation of food substances (mainly sucrose)
- this is from the leaves to the rest of the plant
- it requires energy from respiration
- the transport goes in both directions
What are xylem tubes made of?
dead cells joined end to end with no end walls between them and a hole in the middle
they are strengthened with a material called lignin
What are some key points about
transpiration?
(3)
what?
from where to where?
any requirements?
what direction?
- it is the transportation of water and mineral ions
- this is from the roots to the stem and leaves
- the transport only goes upwards
Define
transpiration stream.
the movement of water from the roots, through the xylem and out of the leaves
How does transpiration work?
(4 steps)
- Transpiration occurs at the leaves.
- This creates a slight shortage of water in the leaf.
- More water is drawn up from the rest of the plant through the xylem vessels to replace it.
- This in turn means more water is drawn up from the roots, and so there’s a constant transpiration stream of water through the plant.
Define
stomata.
the tiny pores on the surface of a plant
What is the purpose of
stomata?
they allow carbon dioxide and oxygen to diffuse directly in and out of a leaf
they also allow water vapour to escape during transpiration
How do guard cells affect the stomata?
when the guard cells are turgid, the stomata are open
when the guard cells are flaccid, the stomata are closed
turgid - swollen with water
flaccid - low on water and limp
What 3 key things affect
transpiration rate?
- light intensity
- temperature
- air flow
How does
light intensity affect the rate of transpiration?
And why?
the brighter the light, the greater the transpiration rate
this is because the stomata begin to close as it gets darker
photosynthesis can’t happen in the dark, so they don’t need to be open to let carbon dioxide in
when the stomata are closed, very little water can escape
How does
temperature affect the rate of transpiration?
And why?
the warmer it is, the faster transpiration happens
this is because when it’s warmer the particles have more energy to evaporate and diffuse out of the stomata
How does
air flow affect the rate of transpiration?
And why?
the better the air flow around a leef, the greater the transpiration rate
this is because if air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away, this means there’s a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn’t happen as quickly, if there’s good air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf, diffusion then happens quickly from an area of higher concentration to an area of lower concentration
State the order of cells in a
typical leaf.
(from top to bottom)
- Waxy cuticle
- Upper epidermis
- Palisade mesophyll tissue
- Spongy mesophyll tissue (+ air space)
- Lower epidermis (+ guard cells and stomata)
How is the
palisade layer adapted for efficient photosynthesis?
(2 things)
- it has lots of chloroplasts
- it is near the top of the leaf, where it can get the most light
How is the
upper epidermis adapted for efficient photosynthesis?
it is transparent so that light can pass through it to the palisade layer
How is the
waxy cuticle adapted for efficient photosynthesis?
it helps to reduce water loss by evaporation
How is the
spongy mesophyll layer adapted for efficient photosynthesis?
it contains air spaces which increase the rate of diffusion of gases into and out of the leaf’s cells
What adaptations do plants living in deserts tend to have?
(to help them conserve water)(6)
- small leaves, or spines instead of leaves
- curled leaves, or hairs on the surface of leaves
- thick waxy cuticles
- a thick, fleshy stem which stores water
- fewer stomata or stomata that only open at night
- stomata sunken in pits
How do small leaves help a plant to conserve water?
this reduces the surface area for water loss by evaporation
How do curled leaves help a plant to conserve water?
this reduces air flow close to the leaf, trapping water vapour near the surface and reducing diffusion from the leaf to the air
How do thick waxy cuticles help a plant to conserve water?
they reduce water loss by evaporation
How do stomata sunken in pits help a plant to conserve water?
this makes the stomata lower than the surface of the leaf, which reduces air flow close to the stomata
Define
auxins.
plant hormones which control growth at the tips of shoots and roots
they move through the plant in solution
How do shoots respond to light?
(name and 2 steps)
they are positively phototrophic (grow towards the light)
1. When a shoot tip is exposed to light, it accumulates more auxin on the side that’s in the shaded than the side that’s in the light.
2. This makes the cells grow (elongate) faster on the shaded side, so the shoot bends towards the light.
How do shoots respond to gravity?
(name and 2 steps)
They are negatively gravitropic (grow away from gravity)
- When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.
- This causes the lower side to grow faster, bending the shoot upwards.
How do roots respond to gravity?
(name and 2 steps)
They are positively gravitropic (grow towards gravity)
- A root growing sideways will also have more auxin on its lower side.
- But in a root the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards.
How do roots respond to light?
(name and 2 steps)
They are negatively phototropic (grow away from light)
- If a root starts being exposed to some light, more auxin accumulates on the more shaded side.
- The auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground.
What are some commercial uses of
plant hormones?
(6 uses)
- selective weedkillers
- growing from cuttings with rooting powder
- controlling flower and fruit formation
- producing seedless fruit
- controlling the ripening of fruits
- controlling seed germination
What are specifically auxins used for commercially?
(2 things)
- selective weedkillers that only affect broad-leafed plants
- rooting powder which allow cutting to produce roots rapidly and start growing as new plants
What are gibberellins used for commercially?
(6 uses)
- making plants flower earlier than they would usually do so
- making plants flower under conditions in which they wouldn’t usually flower
- reducing flower formation which can improve fruit quality
- to allow the fruit in unpollinated flowers to grow (but not the seeds)
- to make sure that seeds will germinate at times of the year that they wouldn’t normally
- to make sure that all the seeds in a batch germinate at the same time
What is ethene used for commercially?
to allow unripe fruits to ripen on the way to the supermarket
