Plant Structures and Their functions Flashcards
Photosynthesis equatioin
carbon dioxide + water –> glucose +oxygen
How are photosynthetic organisms the main producers of food for nearly all life on earth?
- During photosynthesis, photosynthetic organisms, such as green plants and algae use energy from the Sun to make glucose
- Some of the glucose used to make up the organisms biomass
- The energy stored in the biomass works its way through the food chain as animals eat them and each other.
- So photosynthetic organisms are the main porducers of food for nearly all life on Earth
Where does photosynthesis happen?
- Happens inside of chloroplasts which contain chlorophyll which absorbs light
- Energy is transferred to the chloroplast by light
What kind of reaction is photosynthesis?
Endothermic - energy is taken in during the reaction
What are the limiting factors of photosynthesis?
- Light intensity
- Concentration of CO2
- Temperature
How is temperature a limiting factor of photosynthesis?
Affects the rate of photosynthesis because it affects the enzymes involved…
- If temperature is too low, the enzymes needed for photosynthesis work slower
- If temperature is too high, the enzymes it needs for photosynthesis and other reactions will be denatured (happens at around 45 degrees)
How is light a limiting factor of photosynthesis?
- Light transfers the energy needed for photosynthesis
- At first, light intensity and rate of photosynthesis are directly proportional (as the light intensity increases, rate of photosynthesis increases) but is only true up to a certain point
The Inverse Square Law
(Light intensity as a limiting factor)
- The square of the distance from the lamp and the light intensity are inversely proportional to each other
- Written as: light intensity = 1/d²
where d = distance from lamp - Means that if you halve the distance, the light intensity will be four times greater and if you double the distance, the light intesnity will be four times smaller
How is CO² Concentration a limiting factor?
- CO² is one of the raw materials needed for photosynthesis
- As with light intensity, increasing CO² concentration increases the rate of photosynthesis up to a point
- As long as CO² is plentiful in supply, then light or temperature is the limiting factor
How do you investigate the rate of photosynthesis?
1) Source of light is placed at a specific distance from the pondweed
2) The pondweed is left to photosynthesise for a set amount of time
3) As it photosynthesises, the oxygen released will collect in the gas syringe. This allows to accurately measure the volume of oxygen produced
4) the whole experiment is repeated wth the light source at different distances from the pondweed. The rate of oxygen production at each distance can be calculated (volume produced / time taken)
What are some variables in the investigation that need to be controlled?
- The temperature (can be controlled by putting the conical flask in a water bath)
- The carbon dioxide concentration (can be controlled by adding a set amount of sodium hydrogencarbonate to a set volume of water)
What do root hair cells do?
- Have a large surface area with the millions of microscopic hairs on its surface
- Allows it to absorb the maximum amount of water and mineral ions from the soil
- The concentration of mineral ions is normally lower than the cell so active transport is used to absorb mineral ions
- Water is absorbed by osmosis
What are phloem tubes and explain how they are adapted to their function.
Function:
- Sucrose ( made from glucose + starch ) is translocated in the sieve tubes of the pholem tissue.
- Large central channel in each sieve cell is connected to companion cells, through which sucrose solution flows through.
- Companion cells actively pump in or take out sucrose of the sieve tubes.
- As sucrose is pumped into sieve tubes, increased pressure causes it to flow up to growing shoots or down to storage organs.
Adaptations:
- Very small amount of cytoplasm ( and no nucleus ) means there is more room for central channel.
- Holes in the ends of the cell walls allows liquids to flow from one sieve cell to another
- Pores through which sucrose solution can be pumped through.
What are xylem tubes and what do they do?
( Include adaptations )
Function:
- During their development, xylem cells die & their top and bottom cell walls disintergrate.
- This creates a long empty vessel through which water can move easily.
- Xylem vessels are also rigid because of thick side walls and hard lignin.
- This means water pressure inside the vessels does not burst them, also helps to support the plant.
Adaptations:
- Tiny pores allows water and ions to enter and leave xylem vessels.
- Lack of cell walls between cells means water flow isn’t slowed down.
- Having no cytoplasm allowed for a hollow tube to form.
Explain how water and minerals are transported through the plant with transpiration
- Inside the Xylem vessels, is an unbroken chain of water, due to weak forces of attraction between water molecules.
- Water is pulled up the xylem vessels in the stem as water evaporates from the xylem vessels in the leaves
- As water vapour diffuses out of a leaf, more water evporates from the xylem inside the leaf.
What are stomata and what do they do?
- are tiny pores on the surface of the plant, mostly found on the lower surface of leaves
- stomata allow CO2 and oxygen to diffuse directly in and out of a leaf and allow water vapour to escape during transpiration
- plants have stomata so that gases can be exchanged more easily. Because there is more water inside the plant than in the air outside, the water escapes from the leaves through the stomata by diffusion
- stomata surrounded by guard cells, which change shape to control the size of the pore
- when the guard cells are turgid (swollen with water) the stomata are open and when the guard cells are flacid (low on water and limp) the stomata are closed
How does light intensity affect transpiration rate?
- The brighter the light, the greater the transpiration rate.
- Stomata begin to close as it gets darker. Photosynthesis can’t happen in the dark, so they don’t need to be open to let CO2 in.
- When the stomata is closed, very little water can escape
How does temperature affect transpiration rate?
- The warmer it is, the faster transpiration happens
- When it’s warm the water particles have more energy to evaporate and diffuse out of the stomata
How does light air flow affect transpiration rate?
- The better the air flow around a leaf (e.g stronger winds) the greater the transpiration rate
- If air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away, this means there is a high concentration of water particles outside of the leaf as well as inside, meaning diffusion doesn’t happen as quickly
- If there is good air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly, from an area of high concentration to an area of low concentration
How can we estimate transpiration rate?
1) Set up apparatus potometer etc.) and then record the starting position of the air bubble
2) Start a stopwatch and record the distance moved by the bubble per unit time, e.g per hour
3) Calculating the speed of air bubble movement gives an estimate of the transpiration rate (use distance moved / time taken)
How is the plant adapted for photosynthesis?
- Leaves are broad so there is a large surface area exposed to light, which is needed for photosynthesis
- The palisade layer has lots of chloroplasts and are near the top of the leaf to get the most light to turn into energy
- The upper epidermis is transparent so that light pass through it to the palisade layer
- The xylem and phloem form a network of vascular bundles, which provide the leaf with water for photosynthesis and take away the glucose produced.
- The epidermal tissues are covered with waxy cuticle, helps reduce water loss by evaporation, cuticle also helps to stop microorganisms and water entering the leaves
- Irregularly shaped spongy cells do not fit together well and create air spaces, allowing gases to diffuse easily inside a leaf.
How is the plant adapted for gas exchanged?
- the lower epidermis has lots of stomata, which let CO2 diffuse directly into the leaf
- spongy mesophyll tissue contains air spaces which increase the rate of diffusion of gases into an out of the leaf’s cell
How are some plants adapted to live in extreme environments?
Plants living in deserts (like cacti) tend to have adaptations such as:
- small leaves or spines instead of leaves, this reduces the surface area for water loss by evaporation. spines also help to stop animals eating the plant to get water
- curled leaves or hairs on the surface of leaves, this reduces air flow close to the leaf, trapping vapour near the surface and reducing diffusion from the leaf to the air
- thick waxy cuticles, again to reduce water loss by evaporation
- fewer stomata or stomata that only open at night, to reduce water loss by evaporation
- In winter, many decidous plants lose all their leaves, preventing water loss when soil may be frozen.
- Conifers have needle-shaped leaves with a much-smaller surface area & a very thick cuticle . This additionally creates less wind resistance allowing conifers to withstand high winds
What are Auxins?
- plant hormones which control growth at the tips of shoots and roots
- move through the plant in solution (dissolved in water)
- auxin is produced in the tips and diffuses backwards to stimulate the cell elongation process which occurs in the cells just behind the tips
- auxin promotes growth in the shoot, but inhibits growth in the root
- auxins are involved in phototropism and gravitropism
What happens when a shoot tip is exposed to light?
- when exposed to light, a shoot tip accumulates more auxin on the side that’s in the shade rather than the side thats in the light
- this makes the cells grow (elongate) faster on the shaded side, so the shoot bends towards the light
- this is called positive phototropism
What happens when a plant grows in the complete darkness?
- shoots growing completely in the dark will be tall and spindly - the auxin in the tips makes them elongate quickly on all sides
- a taller shoot has a better chance of finding light
How does a shoot become negatively gravitotropic?
- when a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side
- this causes the lower side to grow faster, bending the shoot upwards away from gravity
How does a root become positively gravitropic?
- A root growing sideways will have more auxin on its lower side
- But in a root the extra auxin inhibits growth. this means the cells on top elongate faster, and the root bends downwards
How does a root become negatively phototropic?
- If a root starts being exposed to some light, more auxin accumulates on the more shaded side
- the auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground
Describe the role of Auxins in Gravitropism
- Auxins are also found in root tips, where they have the opposite effect to that in shoots.
- In roots, auxin causes cells to stop elongating and this causes positive gravitropism - growth towards the direction of gravity.
- This is done to help roots to anchor plants in place and reach moisture underground.
How do you investigate plant growth responses?
1) Put some cress seeds in a Petri dish lined with moist filter paper
2) Surround the Petri dish with black card. (e.g a box)
3) Cut a hole in one side of the card only
4) Shine a light into the box through the hole
5) Leave your cress seeds alone for one week until you can observe their response - you should find the seedlings grow towards the light. You can even measure the angle they are growing at
How are auxins used for commercial use?
As selective weedkillers:
- Most weeds are broad leaved in contrast to the very narrow leaved grasses and cereals
- selective weedkillers have been developed using auxins, which only affect the broad-leaved plants
- they totally disrupt their normal growth patterns which soon kills them
Growing from cuttings with rooting powder:
- Normally, if you stick the cuttings of plants in the ground, they will not grow
- If you add rooting powder, which contains auxins, however, they will produce roots rapidly and start growing as new plants
- enables growers to make lots of clones of a really good plant very quickly
What are gibberellins and how are they used for commercial use?
Gibberellins are plant hormones that stimulate seed germination, stem growth and flowering …
Controlling flower and fruit formation:
- can be used to make plants flower earlier than they woul usually do so or under conditions which they wouldn’t usually flower
- can also be used to reduce flower formation, which can improve fruit quality. fewer flowers mean fewer frutis, which are able to grow nice and big
Producing seedless fruit:
- fruit with seeds in the middle normally only grows on flowering plants which have been pollinated by insects. if the flower doesn’t get pollinated, the fruit doesn’t grow
- if plant hormones such as gebberillins are applied to unpollinated flowers, the fruit will grow but the seeds won’t
Describe the commercial use of ethane.
- Unripe fruits are easier to transport than ripe fruits without damaging them.
- The unripe fruit can also be kept for longer without going off.
- Fruit producers often pick un-ripe fruit then just ripen it when needed using a plant hormone called ethene.
