Topic 6: Plant Structures and their Functions Flashcards
What are plant tropisms?
The growth of a plant to in response to a stimulus
What is positive tropism?
The growth of a plant towards a stimulus
What is negative tropism?
The growth of a plant away from a stimulus
What are the two main types of plants tropism?
Phototropism and Gravitropism
What is phototropism?
A plants growth response to light
What is gravitropism?
A plants growth response to gravity
What are auxins?
A group of plant hormones involved in plant tropisms and control growth in plant roots and shoot tips
Compare the effect of auxins in plant shoots and roots
Auxins stimulate growth in plant shoots and auxins inhibit growth in plant roots
Where are auxins produced?
Root and shoot tips
How do auxins move through a plant?
They diffuse through the plant in solution
Are plant shoots positively or negatively phototropic? How does this affect shoot growth?
Positively phototropic and plant shoots grow towards the light
Why do plant shoots are positively phototropic?
Shoot tip exposed to light, on the shaded side of the shoot, auxin accumulates, elongation of cells on the shaded side and shoot tip bends towards the light
Are plant shoots positively or negatively gravitropic? How does this affect shoot growth?
Negatively gravitropic and plant shoots grow upwards, away from gravity
Why are plant shoots are negatively gravitropic?
Shoot placed horizontally, due to gravity, auxin accumulates on the lower side of the shoot, elongation of cells on the lower side and shoot bends upwards growing away from gravity
Are plant roots positively or negatively phototropic? How does this affect roots growth?
Negatively phototropic and plant roots grows away from the light
Why are plant roots negatively phototropic?
Root exposed to light, on the shaded side of the root, auxin accumulates, inhibition of cell growth on the shaded side and root grows away from the light
Are plant roots positively or negatively gravitropic? How does this affect root growth?
Positively gravitropic and plant roots grow downwards, towards gravity
Why are plant roots are positively gravitropic?
Root placed horizontally, due to gravity, auxin accumulates on the lower side of the root, inhibiting of cell growth on the lower side and root bends downwards growing towards gravity
How are plant tropisms increase the chance of survival?
They enable plants to respond to the environment, shoot growth towards the light maximises light absorption, root growth downwards increases the uptake, of water and minerals from the soil and enables anchorage of the plant body to the ground
What is the role of auxins in commercial plant cultivation?
Rooting powders contain auxins that stimulate the growth of roots in cutting, enables rapid plant cloning and used in selective weedkillers that target and alter growth patterns in broad-leaved plants, killing them
What are gibberellins?
Plant hormones that control germination and flowering
What is the role of gibberellins in commercial plant cultivation?
Initiate germination in seeds at times of the year when they naturally wouldn’t, ensure all seeds in a batch germinate, trigger flowering in plants under irregular conditions, also increase fruit size by reducing the number of flowers produced by plants and produce seedless fruits by stimulating the growth of fruit from unpollinated flowers
How do gibberellins trigger germinations?
In the presence of water, gibberellins break seed dormancy, initiating germination
Why is Ethan important in commercial plant cultivation?
Ethane stimulates enzymes that control fruit ripening and enables fruit to be picked while they are unripe and less easily damage, they can be stimulated to ripen during transportation to shops
What is photosynthesis?
A chemical reaction that takes place inside photosynthetic organisms converting light energy into chemical energy
What is the word equation for photosynthesis?
Carbon dioxide + water -> glucose + oxygen
What is the symbol equation for photosynthesis?
6CO2 + 6H20 -> C6H12O6 + 6O2
Why is photosynthesis important?
It produces glucose which has a wide range of uses such as used in respiration to release energy, converted to starch and stored - broken down to glucose when the plant requires energy and used to make complex organic molecules which are used for growth, making up an organisms biomass
Where does photosynthesis take place?
Within chloroplasts
What type of reaction is photosynthesis?
An endothermic reaction that takes in energy
What is chlorophyll?
A pigment found in chloroplasts that absorbed light
What is the two main stages of photosynthesis?
Chlorophyll absorbs light energy which is used to split water into oxygen gas and hydrogen ions then carbon dioxide combines with hydrogen ions to form glucose
What factors affect the rate of photosynthesis?
Temperature, light intensity and carbon dioxide concentration
What is a limiting factor?
A variable that limits the rate of a particular reaction
How does temperature affects the rate of photosynthesis?
Higher temperatures provide more KE for enzymes involved in photosynthesis so the rate increases as temperature rises, the optimum temperature is usually 25C and if the temperature becomes too high enzymes become denatured and the rate of photosynthesis decreases
How does light intensity affect the rate of photosynthesis?
Rate of photosynthesis is directly proportional to light intensity as light intensity increases, the rate of photosynthesis increases
Why does the rate photosynthesis eventually plateau even if light intensity continues to increase?
Another factor becomes limiting
How can the effect of light intensity on the rate of photosynthesis be measured in the lab?
Using a light meter, using the inverse square law where: light intensity = 1 / distance2
Why does the rate of photosynthesis decrease as the distance from a light source increases?
Light intensity is inversely proportional to the square of the distance from the light source, this as the distance increase, light intensity decreases and the rate of photosynthesis decreases
How does carbon dioxide concentration affects the rate of photosynthesis?
As carbon dioxide concentration increases, the rate of photosynthesis increases
Why does the rate of photosynthesis eventually plateau even if CO2 concentration continues to increase?
Another factor becomes limiting
Why do plants require water?
Photosynthesis, maintenance of structures and cooling effect
Why do plants require minerals ions?
For growth
Which structure in plants is adapted for the uptake of water and minerals?
Root hairs
How is water transported into root hairs?
Lower concentration of water in root hair cells than in the soil and water diffuses down its concentration gradient into root hair cells by osmosis
How are minerals transported into root hairs?
Lower concentration of minerals ions in the soil that in the root and root hair cells take up minerals ions by active transport
How does plant roots are adapted for the absorption of water and minerals?
Plant roots are composed of millions of root hair cells which have: long hair that extend from the cell body, increasing the surface area for absorption and many mitochondria which produce ATP for active transport of mineral ions
What are the two plant transport tissues?
Xylem and Phloem
What is the function of the xylem?
Transports water and minerals up the plant, from the roots t o the leaves via the transpiration stream
How is the xylem adapted to its function?
Composed of dead cells laid end-to-end to form a long, hollow continuous column, no end walls which provides little resistance to the passage of water and thick cell wall strengthened with lignin to provide support
What is the function of the phloem?
Transports sugars up and down the stem from photosynthetic tissues to non-photosynthetic tissues via translocation
What are the two cells types that make up the phloem?
Sieve tube elements and companion cells
How is the phloem adapted to its function?
Sieve tube elements are long, thin cells, laid end-to-end with perforated end plates to enable the flow of sugars, they contain no nucleus and little cytoplasm to allow sugars to flow easily and companion cells contain a dense cytoplasm, nucleus and mitochondria, they provide energy for processes in both cell types
What is transpiration?
The loss of water vapour from parts of a plant exposed to the air due to evaporation and diffusion
Where does the majority of transpiration take place?
Leaves
What happens in the process of transpiration?
Water Eva from the mesophyll cell surfaces and diffuses out of the stomata, water molecules are drawn up the xylem vessels to replace the water that has been lost and this causes more water molecules to be absorbed from the soil into root hair cells
How does the transpiration stream transport mineral ions?
Mineral ions are dissolved in the water that is carried by the transpiration steam
What are stomata?
They are pores found in the lower epidermis of a leaf which allow gas exchange
What are guard cells?
Specialised cells surrounding the stomata that change shape to control the size of the pore
How do guard cells control the size of stomata?
To open it: water enters guard cells, they swell and become turgid, they bend and draw away from each other, opening the stomata
To close it: water leaves guard cell, they become flaccid, closing the stomata
What factors affect the rate of transpiration?
Light intensity, temperature and air movement
How does high light intensity affects the rate of transpiration?
High light intensity, greater number of stomata open to allow gas exchange for photosynthesis, rate of photosynthesis increases so more water is taken up from the soil, pushing water up the xylem and more water vapour diffuses out of the stomata so the rate of transpiration increases
How does low light intensity affect the rate of transpiration?
At a low light intensity, fewer stomata are open so the rate of transpiration decreases
How does temperature affects the rate of temperature?
Temperature increases, water molecules have more KE so rate of diffusion increases, photosynthesis also increases so more water is taken up from the soil, pushing water up the xylem and more water vapour diffuses out of the stomata so the rate of transpiration increases
How does air movement affects the rate of temperature?
Air movement increases, high water concentration gradient maintained between the air spaces in the leaf and atmosphere, increased rate of diffusion of water molecules out of the stomata so the rate of transpiration increases
What apparatus is used to measure the rate of transpiration?
Potometer
What is assumed when measuring the rate of transpiration using a potometer?
Rate of water water uptake ≈ rate of transpiration
How can the rate of transpiration be calculated using a potometer?
distance moved by bubble / time taken
What is translocation?
The movement of sugars up and down a plant, from the source to the sink via the phloem (requires ATP)
How are leaves adapted for photosynthesis?
Broad so large SA for light absorption, thin so short diffusion distances for gases allows light to reach all cells, vascular bundles form a network to deliver water and remove glucose and provide support, photosynthesis pigments absorb light
How are tissues of leaves adapted for photosynthesis and gas exchange?
Palisade mesophyll layer so receives most light so contains greatest concentration of chloroplasts, upper epidermal so allows light to react palisade layer, spongy mesophyll layer so air spaces increase the rate of diffusion and lower epidermal so contains many stomata for gas exchange
How are plants adapted to live in hit, dry conditions?
Small leaves/plants so reduce SA for water loss, thick waxy cuticle so reduces evaporation, thick stem so provides storage for water, shale but widespread roots so large SA to absorb water, stomata sunken in pits and leaves curled so reduces air flow, lowering diffusion gradient and reducing water loss by evaporation and stomata close to reduce water loss
