Topic 9: Checklist Questions Flashcards
Outline that transpiration is the inevitable consequence of gas exchange in the leaf.
Result of gas exchange in leaves:
- Stomata opens up
- Gas exchange occurs; oxy in and carbo out
- Due to a concentration gradient between the leaf and the atmosphere, some water diffuses out
This causes transpiration.
- guard cells determine if stomata closed or open
Explain how plants transport water from the roots to the leaves to replace losses from transpiration.
Due to the cohesive property of water, the water is pulled upwards.
Transpiration pull: loss of water vapor through the stomata helps to pull the water from roots all the way up to leaves
Water absorbed through routes via osmosis
Higher concentration of solutes than outside
Water moves along concentration gradient
Explain how the adhesive properties of water and evaporation generate tension forces in leaf cell walls.
- this generates transpiration pull
- causes upward movement of water inside the xylem vessels to the leaves to replenish the water lost through transpiration.
Explain how the cohesive property of water and the structure of the xylem vessels allow transport under tension
Cohesion: water molecules are polar and stick to each other which helps water move up long distances
- lignified xylem
- lignin makes tube stronger
- water sticks to sides of xylem and pulls other molecules up as well
- when water is used or transpired water from the xylem replaces it.
Explain how active uptake of mineral ions in the roots causes absorption of water by osmosis
Water and minerals are taken up by roots, tiny extensions on specialised root cells called root hairs take up water through osmosis. This creates a concentration gradient inside the roots and causes water to diffuse into the roots through osmosis. The concentrations are created through active transport.
Explain the adaptations of plants in deserts and saline soils for water conservation
Number of ways xerophytes can live:
- leaf size reduced
- succulent to store water
- stomata mostly on stem
- stomata open at night
- leaf covered with waxy cuticles
- leaves roll up to reduce evaporation
- spread out root systems to achieve more water
Halophytes conditions on living:
- Reduced leaf sizes
- more water storage
- Thick cuticle and thick epidermis
- Stomata sunk into pits
- Some plants have structures to remove salt build-up
- Root cells pump excess sodium and chloride ions out into the surrounding soil or water
Measure transpiration rates by using potometers.
Potometer: device that is often used in school labs for measuring the rate of transpiration of a leafy plant shoot
Two ways of collecting data:
Measure the water absorbed over a time period
Measure the drop in mass over a fixed amount of time
Explain how plants transport organic compounds from sources to sinks
Sources: photosynthesising tissues and some plant organs that export sugars to other parts of the plant
Acquire substances such as organic substances in leaves
Sinks: plant organs that cannot produce sugars but need them for respiration or storage
Lack of the substances and need some of them through translocation
Outline how incompressibility of water allows transport along hydrostatic pressure gradients
When an organic compound such as sucrose is moved into the Phloem through active transport water moves in as well through osmosis due to the concentration gradient made. However water is not very compressible at all (try squeezing some and see what happens, nothing but a mess) so the addition of water into the phloem results in pressure that moves the organic compound around the plant.
Explain how active transport is used to load organic compounds into phloem sieve tubes at the source.
Phloem : transports sap from sources to sinks
- Mixture of water, carbohydrates, minerals, amino acids and plant hormones
- Ensuring all parts of the plant that performs the functions of life
- Requires active transport
- Resulting high concentrations of carbohydrates need to be contained inside the sieve elements
- Consists of living cells with reduced cytoplasm and no nucleus
- But cells do have membranes to help with concentrations of solutes
Explain the structure–function relationships of phloem sieve tubes.
Sieve elements:
Lose most of their cellular components when they mature
This leads to a tube-like structure that allows sap to flow through easily
Explain how high concentrations of solutes in the phloem at the source lead to water uptake by osmosis.
When solutes are pooled at the source the solution becomes hypertonic in that area. Through osmosis water comes in to maintain equilibrium and as water comes in it pushes the solutes in the phloem away from the source.
Outline that undifferentiated cells in the meristems of plants allow indeterminate growth
Meristems: the tissue in most plants containing undifferentiated cells (meristematic cells)and found in zones of the plant where growth can take place.
Outline that mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves
As the Meristematic cells divide and differentiate, cells needed for growth and the development of the stem and leaves and the root are produced.
Outline that plant hormones control growth in the shoot apex.
Plant hormones:
Hormones are chemical messengers
Small organic molecules that are simpler than animal hormones
In the shoot apex, the top of the plant, a hormone called auxin controls growth. When the plant reacts to a stimulus in the environment the hormone is produced and moved using PIN3 proteins. An example of a stimulus is sunlight, when a side of the plant is exposed to light auxin is produced and then moved to the side that is not facing the sun. The hormone then stimulates growth/mitosis in that area causing the plant to, in this case, grow towards the stimulus.
