2.3 Plant tissues, organs & systems

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Cards (32)

Describe the structure of a leaf
Leaf tissues - epidermis, palisade mesophyll, spongy mesophyll, xylem & phloem
How does the structure of epidermal tissue relate to its function?
● Secretes a waxy cuticle → waterproofs leafs surface, reducing water loss (by evaporation)
● Single layer of transparent cells → allow light to pass through
How does the structure of palisade mesophyll tissue relate to its function?
Many chloroplasts → lots of chlorophyll to maximise light absorption for rapid photosynthesis
How does the structure of spongy mesophyll tissue relate to its function?
Many large air spaces → large surface area for rapid diffusion of gases eg. CO2
, O2
How does the structure of meristem tissue relate to its function?
● Found in growing tips of shoots and roots
● Made up of stem cells → can differentiate into any type of plant cell → allowing plant growth
How does the structure of xylem tissue relate to its function?
Function: transports water and dissolved mineral ions from roots to leaves
● Lignin → strength to withstand pressure of water moving
● Hollow tubes / no cytoplasm → water / mineral ions move easily
● End walls between cells broken down → cells form a long tube so
water / mineral ions flow easily
How does the structure of phloem tissue relate to its function?
Function: transports dissolved sugars (eg. sucrose) from leaves to rest of
plant for immediate use or storage
why is this statement wrong?
“The waxy cuticle is a tissue / made of cells.”
It is not made of cells, so is not a tissue. It is made of lipids.
why is this statement wrong?
“Respiration does not happen in plant cells.”
It happens in cells of all living organisms, to release energy.
why is this statement wrong?
“Xylem only transports water. Ions travel through phloem.”
Xylem transports water and mineral ions eg. magnesium,
nitrate. Phloem transports dissolved sugars.
Describe why it’s important
that dissolved sugars are
moved both upwards and
downwards in a plant. (3)
● Sugars are made in leaves by photosynthesis
● All cells need sugar for respiration
● Sugars transported to meristems for growth / cell division / mitosis
OR sugars transported for storage as starch / fat / oil
xylem?/phloem comp 6
Structure
● Xylem is made of dead cells and phloem is made of living cells
● Phloem cells have pores in their end walls, xylem cells do not
● Xylem is hollow / does not contain cytoplasm, phloem does
● Xylem contains lignin, phloem does not
● Both tubular and made of cells
Function
● Xylem transports water / mineral ions, phloem transports sugars
● Xylem is involved in transpiration, phloem is involved in translocation
● Xylem transports unidirectionally, phloem transports bidirectionally
● Both transport liquids / substances throughout the stem / leaves / roots
Which organs form the system that transports substances around a plant?
Roots, stem and leaves.
Describe the process of transpiration
Evaporation of water from cells inside leaves
2. Diffusion of water vapour out of leaves through stomata
Describe the transport of water and mineral ions through a plant from the
soil to the atmosphere, in the transpiration stream
Water evaporates from cells inside leaves and water vapour diffuses out of leaves through stomata
2. This drives pull of water with dissolved mineral ions up xylem vessels
3. Water enters through root hair cells by osmosis and mineral ions enter by active transport
Describe the role of stomata and guard cells
● Guard cells control size of stomata (pores in epidermis)
● To control gas exchange (CO2
in / O2 out) and water loss from leaves
○ High light intensity → guard cells open stomata (as water enters
guard cells by osmosis so they swell) → allow CO2
in for photosynthesis
○ Hot / dry / low light intensity→ guard cells close stomata (as water
leaves guard cells by osmosis so they shrink) → prevent water loss
explain the effect of increasing this factor on the rate of transpiration
Factor:Light intensity
Increasing it... Increases transpiration rate
Because...
● More stomata open to allow CO2 to enter plant for photosynthesis
● So more water vapour can diffuse out of leaves
explain the effect of increasing this factor on the rate of transpiration
factor:Temp
Increasing it... Increases transpiration rate
Because...
● Increases evaporation of water (due to increased energy)
explain the effect of increasing this factor on the rate of transpiration
factor: Humidity
Increasing it... Decreases transpiration rate
Because...
● Increased water vapour in air
● Reduces concentration gradient (of water vapour) between air and leaf
● So diffusion (of water vapour out of leaf) is slower
How can the rate of transpiration be estimated?
● Use a potometer to measure uptake of water by a plant
○ Assume water uptake is directly related to water
loss by leaves through transpiration
● Set up according to the diagram
● Measure distance travelled by air bubble in fixed period
of time → calculate rate of water uptake
Describe the process of translocation
● Movement of dissolved sugars (eg. sucrose) through phloem (up and down)
● From leaves (made in photosynthesis) to rest of plant for immediate use (eg. respiration) or storage
why is this statement wrong?
“Transpiration is the same as
the transpiration stream.”
Transpiration is the loss of water vapour from leaves. The transpiration
stream is the constant movement of water through the plant.
why is this statement wrong?
“Leaves lose water by osmosis.”
Leaves lose water by transpiration.
why is this statement wrong?
“Water vapour enters leaves
through stomata.”
Water vapour is lost through stomata during transpiration. Water enters
plants through roots and is pulled up to leaves through the xylem.
why is this statement wrong?
“Sugar is taken up from the soil
via roots.”
Plants make their own sugar by photosynthesis in leaves. This travels to the rest of the plant through phloem in translocation.
Explain why a tree might die if the roots of the
tree are damaged. (6)
- Less absorption of water
● Lower rate of photosynthesis so less glucose
● So less respiration / cellulose made for cell walls /
amino acids made for making new proteins
- Less absorption of ions
● Fewer nitrates so fewer proteins made for growth
● Fewer magnesium ions so less chlorophyll
produced so lower rate of photosynthesis
- Damage to phloem
● Less transport of sugars to root cells
● For respiration
- Damage to xylem
● Less water transported
● Fewer nitrates reach cells so fewer proteins made
● Less anchorage
Describe two differences between the
transpiration stream and translocation. (2)
● Transpiration stream involves xylem, translocation
involves phloem
● Transpiration stream transports water (& mineral
ions), translocation transports dissolved sugars
● Transpiration stream moves substances upwards,
translocation moves substances up and down
A teacher used celery to show water uptake in
plants. Celery was left in water with red dye for 3
hours. After, the leaves of the celery were dark
red. Explain how. (3)
● Water / dye moves up plant / stem / celery
● In the xylem
● To the leaf / stomata
Having a large number of stomata per mm2 of
leaf surface can be a disadvantage to a plant. (1)
● More water loss (plant more likely to wilt)
Rate of water loss from leaves at midnight is
much lower than at midday. Explain why. (2)
● Stomata are (almost completely) closed (at night)
● Because it’s cooler / no light
Most plants have more stomata on the lower
surface of a leaf than on the upper surface.
Explain why. (3)
● Cooler around lower surface
● More humid around lower surface
● So less water evaporated
A student used a potometer to investigate the
rate of water uptake in a plant shoot. Explain why
the air bubble would not move if the
investigations were done in the dark. (3)
● No photosynthesis
● So stomata closed (as no CO2 needed)
● So no transpiration