Plant Organisation Flashcards
(16 cards)
The main roles of plant stems and roots are to transport substances around. They have two types of
transport systems
xylem
and
phloem
.
Function of Xylem
transports water and minerals.
Function of Phloem
transports sugars and amino acids dissolved in water.
What are the features of a leaf
Large surface area For maximum absorption of light; for optimum absorption of carbon dioxide
A thin, flattened blade - though there are exceptions So that water and gases have a limited distance to diffuse
Vascular tissue in the midrib and veins Branches of the xylem, to transport water and minerals to the leaf; branches of the phloem, to transport glucose and other products of photosynthesis to other parts of the plant
Air spaces between cells within the leaf For the diffusion of gases
The palisade mesophyll layer of the leaf is adapted to absorb light efficiently. The cells:
are packed with many chloroplasts
are column-shaped and arranged closely together
towards the upper surface of the leaf
What do the Vessels in a xylem do?
Lose their end walls so the xylem forms a continuous, hollow tube.
Become strengthened by a chemical called
lignin
. The cells are no longer alive. Lignin gives strength and support to the plant. We call lignified cells wood.
Is transportation in xylem a physical or chemical process?
Transport in the xylem is a physical process. It does not require energy.
The
phloem
moves food substances that the plant has produced by photosynthesis to where they are needed for processes such as:
growing parts of the plant for immediate use
storage organs such as bulbs and tubers
developing seeds.
Transport in the phloem is therefore both up and down the stem. Transport of substances in the phloem is called ?
Translocation
What are the adaptions of Phloem cells
Sieve tubes
- specialised for transport and have no
nuclei
. Each sieve tube has a perforated end so its
cytoplasm
connects one cell to the next.
Companion cells
- transport of substances in the phloem requires energy. One or more companion cells attached to each sieve tube provide this energy. A sieve tube is completely dependent on its companion cell(s)
When the plant opens its stomata to let in carbon dioxide, water on the surface of the cells of the
spongy mesophyll
and
palisade mesophyll
evaporates
and
diffuses
out of the leaf
transpiration
Water uptake
Root hairs are single-celled extensions of
epidermal cells
in the root. They grow between soil particles and absorb water and minerals from the soil.
Water enters the root hair cells by osmosis. This happens because soil water has a higher water potential than the cytoplasm of the root hair cell. Minerals enter by
active transport
.
Factors affecting transpiration
temperature
humidity
air movement
light intensity
How they affect transpirtation
An increase in temperature increases evaporation, so the rate of diffusion of water from inside the leaf to outside increases
A decrease in humidity reduces the concentration of water molecules outside the leaf, so the rate of diffusion of water from inside the leaf to outside increases
An increase in air movement removes water vapour from outside the leaf, so the rate of diffusion of water from inside the leaf to outside increases
An increase in light intensity generally increases the number of open stomata, so the rate of diffusion of water from inside the leaf to outside increases
How to measure water uptake
The potometer is filled with water.
A shoot is cut from a woody plant. The end of the shoot is cut under water to ensure that the xylem remains water-filled and prevents air locks.
The shoot is inserted into the rubber tubing at the end of the potometer.
The potometer is raised so that a bubble of air is taken up.
The potometer is lowered into the water. The distance travelled by the air bubble is recorded over a period of time.
Variables
Independent variable - time
Dependent variable - the distance moved by the bubble along the capillary tube
Control variables - temperature, air flow or draughts, adequate supply of water
