Topic 6 - Plant Structures and their functions Flashcards
How does temperature affect the rate of transpiration?
The warmer it is, the greater the rate of transpiration. When it’s warm, the water particles have more energy to evaporate and diffuse out of the stomata.
Describe the method of the investigation of the effect of light intensity on the rate of photosynthesis. (6)
1) The gas syringe should be empty to start with. Sodium hydrogencarbonate may be added to the water to make sure it has sufficient carbon dioxide (sodium hydrogen carbonate releases CO2 in solution).
2) A source of white light is placed at a specific distance from the pondweed.
3) The pond is left to photosynthesise for a set amount of time.
4) As it photosynthesises, the oxygen released wants to collect in the gas syringe. This allows you to accurately measure the volume of oxygen produced.
5) The whole experiment is repeated with the light source at different distances from the pondweed. The rate of oxygen produced at each distance can be calculated .
6) For this experiment, any variable that could affect the results should be controlled, e.g. the temperature (which can be controlled by putting the conical flask in a water bath) and the carbon dioxide concentration (which can be controlled by adding a set amount of sodium bicarbonate to a set volume of water).
How are auxins used commercially?
Selective weed killers kill some plants, but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass. The selective weed killer contains auxins which causes the weeds to grow too quickly and die. Because the weeds have broader leaves, the weed killer is absorbed in larger quantities by the weeds than it is by the grass. Selective weed killers can reduce biodiversity within treated areas due to specific plants being killed.
Rooting powder also contains auxins to promote growth. A small potted plant bring dipped in rooting powder Plant cuttings can be dipped Selective weed killers kill some plants, but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass. The selective weed killer contains a growth hormone that causes the weeds to grow too quickly and die. Because the weeds have broader leaves, the weed killer is absorbed in larger quantities by the weeds than it is by the grass. Selective weed killers can reduce biodiversity within treated areas due to specific plants being killed.
Rooting powder contains plant hormones to promote growth.
A small potted plant bring dipped in rooting powder
Plant cuttings can be dipped Selective weed killers kill some plants, but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass. The selective weed killer contains a growth hormone that causes the weeds to grow too quickly and die. Because the weeds have broader leaves, the weed killer is absorbed in larger quantities by the weeds than it is by the grass. Selective weed killers can reduce biodiversity within treated areas due to specific plants being killed.
Rooting powder contains plant hormones to promote growth. A small potted plant bring dipped in rooting powder. Plant cuttings can be dipped in hormone rooting powder before planting.
How can you calculate the transpiration rate?
Distance moved ÷ time taken
How is sucrose transported around the body?
Phloem transports sucrose and amino acids up and down the plant. This is called translocation. In general, this happens between where these substances are made (the sources) and where they are used or stored (the sinks).
This means, for example, that sucrose is transported:
- from sources in the root to sinks in the leaves in spring time
- from sources in the leaves to sinks in the root in the summer
How does not enough light slow down the rate of photosynthesis?
Light transfers the energy needed for photosynthesis. As the light level is raised, the rate of photosynthesis increases steadily(the rate is directly proportional to the light intensity). But this is only until a certain point where afterwards it doesn’t affect it and it will either be temperature or CO2 level that affects it. The distance from the lamp and light intensity are inversely proportional to each other. However, light intensity decreases in proportion to the square of the distance. This is called the inverse square law
Explain how water and mineral ions are transported through the plant by transpiration
Transpiration is caused by the evaporation and diffusion of water from a plant’s surface. Most transpiration happens at the leaves. The loss of water oreates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it. This in turn means more water is drawn up from the roots, and so there’s a constant transpiration stream of water through the plant. The transpiration stream carries mineral ions that are dissolved in the water along with it.
How is the structure of a leaf adapted to photosynthesis and gas exchange?
- Broad so there is a large surface area exposed to light which is needed for photosynthesis
- The Palisade layer has lots of chloroplast, near the top of the leaf so they can get the most light.
- The upper epidermis is transparent so light can get to the palisade layer
- The xylem and phloem provide provide the leaf with water and take away the glucose produced; and they support the structure.
- The epidermal tissues are covered with a waxy cuticle to reduce water loss
- The lower epidermis as lots of stomata which lets Carbon Dioxide diffuse directly into the leaf. The spongy mesophyll has air spaces which increase the rate of diffusion of gases in and out of leaf cells.
What can be use to investigate the effect of light intensity on the rate of photosynthesis?
Canadian pondweed (an aquatic plant) can be used to measure the effeot of light on the rate of photosunthesis. The rate at which the pondweed produces oxygen at the rate at which it’s photosynthesising - the faster the rate of oxygen production, the faster the rate of photosynthesis.
What is type of reaction is photosynthesis in plants and algae?
An endothermic reaction that uses light energy to react carbon dioxide and water to produce glucose and oxygen
Describe photosynthetic organsisms
During photosynthesis, photosynthetic organisms, such as green plants and algae, use energy from the Sun to make glucose. Some of the glucose is used to make larger, complex molecules that the plants or algae need to grow. These make up the organism’s biomass- the mass of living material. The energy stored in the organisms’ biomass then works its way through the food chain as animals eat them and each other. So photosynthetic organisms are the main producers of food for nearly all life on Earth.
How do shoots grow in response to light and gravity?
SHOOTS ARE POSITIVELY PHOTOTROPIC (grow towards light)
1) When a shoot tip is exposed to light, it accumulates more auxin on the side that’s in the shade than the side that’s in the light.
2) This makes the cells grow (elongate) faster on the shaded side, so the shoot bends towards the light.
By bending towards the light, the shoot will be able to absorb more light for photosynthesis, which enables the plant to grow. 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.
SHOOTS ARE NEGATIVELY GRAVITROPIC (grow away from gravity)
1) When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.
2) This causes the lower side to faster, bending the shoot upwards.
Describe what Phloem tubes do and how they are adapted to their function.
Phloem tubes are made of columns of living cells. They transport food substances (mainly sucrose) made in the leaves to the rest of the plant for immediate use or storage. This process is called translocation and requires energy from respiration. The transport goes in both directions.
How do roots grow in response to light and gravity?
ROOTS ARE POSITIVELY GRAVITROPIC (grow towards gravity)
1) A root growing sideways will also have more auxin on its lower side.
2) But in a root the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards.
ROOTS ARE NEGATIVELY PHOTOTROPIC (grow away from light)
1) If a root starts being exposed to some light, more auxin accumulates on the more shaded side.
2) The auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground. Roots that are underground aren’t exposed to light. They grow downwards due to positive gravitropism.
What are the limiting factors of photosynthesis?
Light intensity, Concentration of CO2 and the temperature affects the rate of photosynthesis.
