Regulatory mechanisms in Plants Flashcards
In plants, what is the primary organ of photosynthesis?
Plant leaves
What is the purpose of pores in plants?
They allow CO2 in and O2 out (air movement for gas exchange)
What is another name of pores?
Stomata
What is the problem with stomata being open?
Allows water vapour to escape
What is the loss of water vapour called?
Transpiration
How do plants minimise water losses?
By using guard cells to open and close stomata at certain times of the day
What do stems in plants do?
Supports leaves and transports organic materials (sugars), ions and water between the root and the leaves
What is at the top of each stem?
Terminal bud
What is at the axis of each new leaf?
Axillary bud
Where does mitosis occur in plants?
The terminal bud and axillary bud
What is the definition of stomata?
The pores through which gas exchange occurs
Where is the stomata usually found?
The epidermis (outer most layer of plants) of the leaf
What does each stoma consist of?
Two elongated guard cells
What causes a change in the stomata being open or closed?
Change in turgor pressure of the guard cells
What is the status of the stoma when then guard cells are turgid?
Pores open
What is the status of the stoma when then guard cells are flaccid?
Pores closed
When are stomata usually open?
During the day
When are stomata usually closed?
During the night
What is the environment of a saguaro cactus?
Harsh desert
What are the skin adaptations of the saguaro cactus?
Skin is covered with a thick, wavy coating that is waterproof, thus reducing water loss via transpiration
Skin is covered with hard spines and flexible bristles, which defend the water stored inside
How do plants replace water losses through transpiration?
Transporting water from the roots to the leaves
What does the root system provide?
Huge surface area to take in water
What are the three forces water in plants is under in xylem tubes?
- A pulling force by transpiration in leaves
- A pushing force exerted by osmosis and entry of water into root hair cells
- Adhesion and cohesion forces of water molecules (work against gravity)
What is the transpiration stream?
A unbroken water of water travelling from roots to leaves in xylem tubes, generated by the three forces
How is osmosis involved in the process of transporting water?
The water from the soil osmoses into the roots, which starts the whole process. The root system creates a massive surface area in which the plants draw in essential ions and water. This high SA is created by root hairs, extensions of epidermal cells that are short lived
What allows the water to transport under tension?
The cohesive property of water and the structure of xylem vessels
What is a xylem vessel?
A long, hollow tube composed of xylem cells
What the features of xylem cells?
Dead at functional maturity.
No cellular components (cytoplasm, membranes, etc)/
What are the types of processes that create the flow of water along xylem vessels?
Passive processes
What is the difference in pressure between inside xylem vessels and the atmosphere?
The pressure inside xylem vessels is usually much lower than atmospheric pressure
What are the features of the walls of xylem vessels?
They are thickened and contain the polymer lignin, which strengthens the walls (so they can withstand very low pressures without collapsing inwards)
Are water molecules polar or non-polar?
Polar
Why do water molecules exhibit cohesion between each other?
Hydrogen bonding
When do water molecules exhibit adhesion?
To hydrophilic cellulose fibres in xylem walls (due to hydrogen bonding)
What occurs as a result of connections between water molecules, and between water and the xylem vessels?
Water can be pulled up in a continuous stream
What is the size of xylem tubes?
Very thin, microspoic
What is the effect of the xylem tubes being small?
A very small amount of water can move a long distance within it
What generates tension forces in leaf cell walls?
Adhesive property of water and evaporation
What happens when water evaporates from the surface of a cell wall in a leaf?
Adhesion causes the water to be drawn through the cell wall to replace the transpiraton. The nearest available source is xylem vessels in leaf veins
How does water move betweeen cells?
osmosis
What is a transpiration pull?
A force generated by a low internal pressure of xylem vessels. It is transmitted through the water in the xylem vessels down the stem and to the ends of the xylem in the roots
What causes a low internal pressure of xylem vessels?
Evaporation of water from leaves and the resulting movement of water out of the xylem
What is the only energy required to drive the transpiration process?
Heat change that causes evaporation and leads to transpiration
What are the two pathways water can take to reach the xylem?
Cytoplasmic/symplastic pathway + extracellular/apoplastic pathway via cell walls
How can mineral ions enter the plants’ systems?
Can be absorbed by active transport or when they dissolve into water and diffuse
How does light affect transpiration?
It is essential for water vapour to be lost through evaporation
What does an increase in light lead to?
An increase in transpiration
What does an increase in temperature lead to?
An increase in transpiration
How does temperature affect transpiration?
Causes the evaporation of water molecules
How does wind affect transpiration?
Moves water molecules away from stomata, increasing water concentration gradient
What does increased wind lead to?
Increase transpiration
How does humid air affect transpiration?
Decreases water vapour gradient
What does high humidity lead to?
Decreased transpiration
What are xerophytes?
Organisms that live in environments characterized by water scarcity and shortage
Which plants are highly adapted to water scarcity and shortage?
Desert plants
What is water in plants needed for?
Support, photosynthesis, transport, cooling, enzyme action
What are the adaptations of xerophytes focused on?
Increased rate of water uptake from soil + reducing the rate of water loss by transpiration
Why do some xerophytes have short reproductive cycles?
To take advantage of what short periods of rain there might be
What is translocation?
The movement of manufactured food (sugars, amino acids, etc)
Where does translocation occur?
In the phloem tissue of vascular bundles
Where does translocation first go to?
Areas of new growth. As the plant ages, it is increasingly transported to sites of storage
Where are amino acids mainly made?
In the roots
Where are amino acids transported to?
Sites of protein synthesis
What does phloem tissue have a relatively high rate of during transport?
Aerobic respiration, as translocation is an active process
Where do water and solutes travel?
Down the hydrostatic gradient to the sink (root cell) where pressure is low.
Why do root cells (the sink) have low pressure?
Active unloading of sucrose: thus loss of water via osmosis
Why do plants have long roots?
Long roots help anchor plant to the sandy desert, preventing it from being rooted out by the wind. Also helps with osmosis and water uptake
What is the survival advantage of having extremely reduced leaves becoming spines?
Reduced leaf area for transpiration and protection against animals
What is the survival advantage of green stems (due to photosynthetic cells in stem tissue)?
Cells carry out photosynthesis to compensate for the reduced leaf size and area
What is the survival advantage of pleats in the stem?
Allows expansion when water storage tissue expands
What is the survival advantage of stems that contain water storage tissue?
Stores water during rainfall to keep plants alive during periods of dryness
What is the survival advantage of having a thick waxy cuticle?
Prevent movement of water out of epidermis
What is the survival advantage of stomata in plant stems (through more widely-spaced than in leaves)?
Allows movement of gases necessary for photosynthesis and respiration
What is the survival advantage of having stomata open at night?
Transpiration occurs more slowly in cooler temperatures
What is the survival advantage of CO2 being absorbed at night (then stored as malic acid - a four-carbon compound)?
CO2 can be released from malic acid during the day, so stomata can remain closed
What is an adaptation specific to Marram grass?
Their leaves roll up to limit water loss, which deals with the drying effects of the wind and tolerating the poor water retention of the soil
How is the stomata put into an enclosed space with Marram grass?
The thick, waxy epidermis extends all the way around as the leaf rolls ups. This prevents the stomata from being near the wind
Where are the stomata located in Marram grass?
They are in pits which allows boundary layers of humidity to build up, reducing water loss by evaporation
What is the effect of having hairs on the inner surface (Marram grass)?
Allows water vapour to be retained, reducing water loss through pores
What does the groove formed by the rolled leaf (Marram grass) do?
Acts as a channel for rainwater to drain directly to the specific root of the grass stem
Where do the sugars of translocation move to?
Flow down the hydrostatic gradient to the sink where the pressure is relatively low.
