9. Plant Biology Flashcards
Define photosynthesis.
Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water.
What does photosynthesis require?
- Carbon dioxide and Water to produce carbohydrates and oxygen
- Oxygen for respiration
What are stoma?
Stomata are tiny pores on leaves, usually on the underside.
What is the function of guard cells?
Two guard cells surround the stoma and they control where it is open or closed and control gas exchange
What is transpiration?
Transpiration is the take up of water by roots and carried through the plant to leaves for release of water vapor.
How does transpiration occur?
- stomata opens up
- gas exchange occurs; oxygen desorbed carbon dio absorbed
- Due to a concentration gradient between the leaf and the atmosphere, some water diffuses out
This causes transpiration.
Why is transpiration essential for plants?
- provide raw materials for photosynthesis
- cool the leaves
- transport the minerals to leaves for use in synthesis of important molecules
What happens if the plant does not replace the water lost during transpiration?
The plant will wilt and will not be able to photosynthesize efficiently
What is the transpiration pull? And what happens during transpiration pull?
Transpiration pull: loss of water vapor through the stomata helps to pull the water from roots all the way up to leaves
Due to the cohesive property of water, the water is pulled upwards. Water absorbed through routes via osmosis
Higher concentration of solutes than outside
Water moves along concentration gradient
Explain the structure and function of xylem tubes.
Xylem transports water from the roots to all other parts of the plant.
- The xylem tubes are long continuous tubes that run from the roots through the stems of plants.
- Walls: thickened with lignin ( a woody tissue)
What are lignins?
It is a woody tissue that prevents the walls of the xylem from collapsing under pressure and adds strength to the woody material of older plants.
What are primary xylem vessels?
Primary xylem vessles are the first xylem that forms from the root or shoot tip and their walls contain very little lignin in the form of annular and spiral thickening
Why are lignin bound to break?
Due to the atmospheric pressure being higher than the pressure within.
What happens once the xylem is matured?
- They lose their cytoplasmic content
- Converted to hollow tubes that transport water within the plant
- Flow of water is driven by passive forces
Explain the process of transpiration.
- The adhesive properties of water, together with evaporation, creates tension forces in leaf cell walls that generate the transpiration pull
This causes the upward movement of water inside the xylem vessels to the leaves to replenish the water lost through transpiration.
What are the two forces?
Cohesion: water molecules are polar and stick to each other which helps water move up long distances
Adhesion: interaction between water and the wall of the xylem vessel
These forces creates a continuous stream of water through the plant
How is lignin used for structural under tension?
The long continuous tubes are lignified
The lignin makes the walls of xylem which prevents the tubes from collapsing
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.
What are the two ways of water movement to the xylem?
Through the apoplast: water moves through the cell walls of the epidermal cells of the root.
Through the symplast: water moves through the cytoplasm of epidermal cells of the root
What is the casparian strip?
It is a band of suberin, a waxy substance that is impermeable to water.
Where is the casparian strip found?
Found in the cell walls of the endodermis of plant roots.
How does water flow from the endodermis and onwards?
Water flows through the symplast pathways to reach the xylem vessels.
How are minerals transported in plants?
- by active transport
- Protein pumps in the plasma membrane of the root hair cells actively pump minerals into the cytoplasm
- Minerals are transported while dissolve in water to the xylem vessels
Define Xerophytes and Halophytes.
Xerophytes: plants that are adapted to thrive under dry conditions eg. cacti
Halophytes: plants that are adapted to living near the sea and have evolved mechanisms to cope with high levels of salt
What are adaptations of xerophytes?
- reduced leaf size
- succulents store more water
- stomata mostly on stem
- stomata open up at night
- leaf coated with waxy cuticles
- leaves rolled up to increase humidity around stomata
- extensive shallow network of roots to absorb more water
What are the adaptations of Halophytes?
- reduced leaf sizes
- Water storage structures develop in the leaves
- 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
What is the crassulacean acid metabolism?
To help with helping the plant not run out of carbon dioxide overnight when the stomata opens
Night: Carbon dioxide is absorbed and converted into malic acid
Day: Carbon dioxide is released and used for carbon fixation in the light-independent reactions.
How can rate of transpiration be determined?
By measuring the amount of water lost from a plant per unit time.
What are the 4 internal factors that affect the rate of transpiration?
- Root to shoot ratio
- Surface area of leaves
- Number of stomata
- Structure of leaf
What are the 4 external factors that affect the rate of transpiration?
Light Wind Temperature Humidity Water supply
How does light effect plant transpiration?
Increased light intensity = increased rate of transpiration due to stomata opening and mroe water vapor escaping
How does wind effect plant transpiration?
Increased wind velocity = increased rate of transpiration due to humid air carried away faster and replaced by drier air.
This increases the rate of transpiration due to steep diffusion gradient of water vapor between air spaces in leaves and environment.
What happens if there is no wind?
There is more humidity in air so it reduces the water vapor to the surrounding air and reduces the rate. But if there is a high velocity of wind, reduced rate because stomata close up.
How does temperature effect plant transpiration?
Increased temperature = increased rate of transpiration
Higher temperature = provides more energy for evaporation of water from cell surfaces and decreases the humidity of the external temperature
Really high temp = stomata close and reduced rate
How does temperature effect plant transpiration?
Higher humidity = higher rate of transpiration
The gradient for diffusion of water vapor from stomata is not steep.
How does water affect plant transpiration?
Decreased water in soil = decreased rate of transpiration
If the roots cant keep up with the rate of transpiration, stomata close, leaf cells lose their turgidity and this reduces the rate.
What are sieve plates and sieve elements?
Sieve plates: perforated end walls
Sieve elements: the elongated living cells that form the phloem tissue
Connected end to end to form a sieve tube
What are sources and 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
Steps of translocation:
EWWW
What is the function of phloem tubes?
- transports sap from sources to sinks
Sap is the mixture of water, carbohydrates, minerals, amino acids and plant hormones - Ensuring all parts of the plant that performs the functions of life
What type of process does the transport of sap from source to sink require?
Active transport.
What are companion cells?
They perform many of the genetic and metabolic functions of the sieve elements or sieve tube cells.
So that the sieve tube cell can maintain the membrane structure necessary for the high solute concentrations
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.
Compare the phloem and xylem tubes.
Phloem:
- living cells
- transport sugars, hormones, proteins
- has companion cells
- sieve tubes have sieve plates that control sap flow
Xylem:
- dead cells
- transport water, minerals
- lignin
- continuous hollow tube
Explain the dicot stem.
Ground tissue is differentiated into different layers such as the cortex and the pith
Vascular bundles are arranged in a ring towards near the edge of the stem
Explain the monocot root.
Monocot root:
The ground tissue is not differentiated into different layers of tissue
Vascular bundles are scattered randomly in the ground tissue
Define meristems and state the function.
Meristems: the tissue in most plants containing undifferentiated cells (meristematic cells)and found in zones of the plant where growth can take place.
Meristems produce continuous cell production.
What are the two main areas where growth can occur?
Root tip and shoot tip.
These are called apical meristems.
What happens to new cells when meristems produce continuous cells?
The new cells are immediately pushed away from the meristematic zone then towards the zone of elongation and then to the zone of differentiation
Why does plants grow continuously?
Due to the continuous production of new cells by the undifferentiated cells in meristems.
What are plant hormones?
They are small organic molecules that act as chemical messengers.
State one difference and similarity of animal and plant hormones.
Similarity:
They are effective at low concentrations
Difference:
Action can be restricted by the transport system as their site of production and site of action can differ
State the function of IAA.
IAA inhibits the growth of axillary side buds causing the plant to grow vertically upwards to trap more light for photosynthesis. This is known as apical dominance
What is apical dominance?
Apical dominance: the inhibition of the growth of axillary side buds so that the plant can grow vertically upwards to trap more light for photosynthesis
What is cytokinin and what does it do?
Plant hormone produced in the root of a plant that promotes the growth of axillary buds
Explain how plant shoots respond to the environment by tropisms, phototropism and geotropism.
Both can be positive, which is growth towards the stimulus or negative, which is growth away from the stimulus.
Shoots show positive phototropism and negative gravitropism.
Grow directly towards the source of light and away from gravity
Shoots receive maximum light for photosynthesis
What makes shoots and roots respond in the way they do to light and gravity?
In both cases, the unequal distribution of auxin has been found to be the cause.
How do shoots grow?
Shoots:
Auxin produced at the shoot tip diffuses towards the zone of elongation and is evenly redistributed
Cells grow at the same rate causing the shoot to extend vertically upwards
More light = grows faster because more auxin concentration
Thus the shoot bend towards the light source
How do roots grow?
Roots:
Plant positioned horizontally
Light from above and gravity from below will cause accumulation of auxin on the below.
This causes inhibition on below, and elongation on upper
This causes the bending of the root towards gravity
What is phototropism?
Regulated by proteins called phototropins
Phototropins regulate the transcription of genes that may play a role in the transport of auxin
Why do plants produce the two proteins?
To support the passing in and out of the layers and moving vertically down the stem
Briefly explain about the auxin influx proteins.
- Found at the top part of the cell
- To take in auxin into the stem
Briefly explain about the auxin effux proteins.
- Found at the basal membrane (base)
- To remove auxin
Explain the process of cell to cell movement of auxin.
- Under normal light conditions, auxin pumped into a cell by mersitem, exits the cell
- The removed auxin re-pumped into cell below
- Auxin moves down the stem with the help of auxin efflux pumps that creates concentration gradients of auxin in plant tissue : highest concentration is at the meristem and the base of the plant
What happens to the plant when light just shines at one side?
Auxin efflux proteins redistribute the auxin laterally towards the shaded part of the cell
So any auxin entering the cell from the apex is pumped out laterally towards the neighbouring cell, which responds by elongating
Thus, causing the bending of the shoot and grow towards the light
How does auxin influence cell growth rates by changing the pattern of gene expression
- Changing the pattern of gene expression
- Enhances the expression of genes that code for wall loosening enzymes and expansin proteins
- They go into the cell wall and are activated in the presence of hydrogen ions to break certain bonds to loosen the wall
- This causes the cell to expand
How does micropropagation work?
Involves the use of tissue culture techniques where plants are grown under controlled conditions from meristematic tissue or somatic cells on nutrient media in vitro
How is micropagation used?
- replication of desirable plants
- to preserve rare species by replicating strands that survive better in their environment and by planting many of them.
Differentiate between pollination, fertilisation and seed dispersal.
Pollination: the transfer of pollen from the anthers of a flower to the stigma of the same flower or of another flower.
Fertilization: the union of male and female gametes (pollen and egg), to form a zygote
Seed Dispersal: the movement or transport of seeds away from the parent plant. (eg. by animals or by wind)
Explain the mutualistic relationships with pollinators in sexual reproduction.
Carried from the anther to the stigma either by wind or animals.
Example of mutualistic relationship: both parties benefit
What happens when one of the species of a mutualistic relationship changes?
Pollination may not be possible and this could lead to extinction of both species
How does fertilisation work in plants?
The pollen grain penetrates the stigma and grows a tube that grows down ovary.
Ovary where the egg cell is fertilised
Occurs in ovule
How can seeds be dispersed?
Eaten by animals and excreted by faeces By wind By water Attached to the fur of animals Sometimes the whole fruit is dispersed.
List the 11 structures of a flower.
- Pistil
- stigma
- style
- ovary
- ovule
- stamen
- stamen
- filament
- petal
- sepal
- peduncle
What does a seed normally contain? (More on notes)
Radicle Plumule One or two cotyledons Testa Hilum Micropyle
List the factors that affect germination.
Seeds: need water, O2, light
Water: uptake of water by dry seeds start the germination process
Oxygen: seeds absorb
Temperature: suitable for metabolic reactions
