Plant tissues, organs and systems (2.3) (M) Flashcards
What type of organ is the leaf?
a plant organ
That the roots, stem and leaves work together in an (…) that (…) substances.
organ system
transports
5 needed
What are the tissues of the leaf?
- upper and lower epidermal tissues
- palisade mesophyll
- spongy mesophyll
- xylem and phloem
- meristem tissue found at the growing tips of shoots and roots
What are guard cells?
specialised cells which control the opening and closing of the stomata to enable gaseous exchange
this may allow CO2 to enter for more/a greater rate of photosynthesis
What does the palisade mesophyll contain and how is it adapted to function?
That the palisade mesophyll contains palisade cells.
It is the site for photosynthesis and the cells have a large number of chloroplasts (containing much chlorophyll so is adapted to absorb as much light as possible.
What does the spongy mesophyll contain and how is it adapted to function?
That the spongy mesophyll has air spaces to create a large surface area for more efficient/greater gas exchange
Where is the meristem tissue found and what can it do?
That meristem tissue is found at the tips of the growing regions of plants and can differentiate into different types of plant cell.
Label a leaf?
sunlight shines on upper epidermis
The phloem and xylem are often found in what?
they are often found together in vascular bundles (veins you can see on leaf)
What is translocation?
the transport of dissolved food (e.g. sucrose, a sugar) from the leaves to other parts of the plant
Where does translocation occur?
the phloem
How is the phloem adapted to function?
Phloem is composed of tubes of elongated cells.
- Cell sap can move from one phloem cell to the next through pores (sieve plates) in the end walls
- have companion cells (containing many mitochondria for energy) to enable the dissolved food to be transported and pass through sieve plates
What does the xylem do?
transports water (transpiration stream - uninterrupted from roots to leaves) and minerals from roots to leaves
2 ways
How is the xylem adapted to function?
- Made up of hollow continuous tubes of dead cells with no end (cell) walls so water can be transported quickly through the cell
- Strengthened by spirals of waterproof lignin - will not absorb water (as made up of dead cells, it needs strengthening)
What does water do to a cell?
Keeps it turgid (not flaccid)
What are factors that increase the rate of transpiration?
- higher light intensity
- higher temperature
- increased airflow
- lower humidity
How does an increased temperature affect the rate of transpiration? How?
increases it
increases molecular movement so that more water molecules evaporate from cell surfaces
there is increased movement of water molecules by osmosis from the leaf to outside of the leaf increases; so more evaporation of water from the stomata
How does an increased humidity affect the rate of transpiration? How?
decreases it
More concentrated solution in leaf, so decreased movement of water molecules by osmosis from the leaf to outside of the leaf (more dilute solution) decreases as the air contains more water molecules (is more dilute), so less water loss as less water is evaporated from the stomata
How does increased airflow affect the rate of transpiration? How?
increases it
Removes water vapour from leaf surfaces, so increased movement of water molecules by osmosis from the leaf (more dilute solution) to outside of the leaf (more concentrated solution) increases, so increased evaporation from stomata
How does increased light intensity affect the rate of transpiration? How?
increases it
The stomata open wider to allow more carbon dioxide into the leaf for photosynthesis
so increased movement of water molecules by osmosis from the leaf (more dilute solution) to outside of the leaf (more concentrated solution) increases, thus more evaporation from stomata so more water loss
What is a potometer used to do?
to investigate the rate of water uptake by a plant
What is the waxy cuticle? What does it do?
A waxy waterproof layer which reduces water loss, it is transparent to allow light through the leaf
Also locks air flow across leaf’s surface - so decreases rate of transpiration
When light intensity is high, potassium ions are moved into guard cells.
How does increased light intensity cause increased transpiration?
potassium ions make the cell more concentrated
water moves into the guard cell by osmosis
cells swell unevenly
as inner wall less flexible than outer wall
This can be applied to any situation relating to increased osmosis into the cell - make sure you understand this
Suggest why leaves took in oxygen during the dark
oxygen used in aerobic respiration
What is the advantage to the plant of the stomata’s width changing over a ten hour period?
reduces rate of transpiration
reduces wilting
The lower surfaces of the leaf were covered in grease, explain why there was no water loss after this
lower surface has most stomata
stomata now blocked by grease
so water cannot escape/evaporate from the stomata
What is transpiration?
Loss of water due to evaporation from the stomata
What is the transpiration stream?
The movement of water molecules from roots to the leaves in the xylem
Water evaporates via the stomata in the leaf tissue
2 marker
How does water move from roots to leaves?
By transpiration stream in xylem
2 marks
A plant has very few stomata on the upper surface of the leaf - how is this an advantage to the plant?
less water lost
do does not wilt
How is the volume of water lost from the leaves controlled?
By the opening and closing of stomata
4 marks
Why do plants need two different methods to absorb water (osmosis) and ions (active transport)?
solution in the soil is more dilute
so water moves from dilute to more concentrated region/solution
concentration of ions less (than that in root hair cells)
so energy need to move ions or ions are moved against concentration gradient
What is the function of the stomata?
(it opens and closes) to allow carbon dioxide to enter and oxygen to leave (i.e. to enable gaseous exchange)
What are three environmental factors that could have increased the rate of transpiration?
- It was warmer
- It was windier
- It was less humid
- or there was more water (vapour) in the leaves
