Unit 4 - Biology: Plants, hormones and reproduction Flashcards
State the functions of xylem and phloem
Xylem: water and soluble salts transport. Water moves the soil to the xylem in the root down a concentration gradient. Water moves up the xylem by CAPILLARY ACTION. One-way flow. Cells dead.
Phloem: organic materials transport from the leaves to all other parts of the plant (eg leave to roots, leaves to developing fruit). Two-way flow. Cells are alive.
Identify the positions of xylem tissues as seen in transverse sections of unthickened, herbaceous, dicotyledonous roots, stems and leaves.
Draw the diagrams
Identify root hair cells, as seen under the light microscope, and describe their functions; relate their structure & function to their surface area and to water and ion uptake.
Draw root hair diagram
Function: absorbs water and mineral ions from the soil.
Large surface area - more area for osmosis
- more water and ions absorbed
- more friction: - stays in ground
- stable
-provides stability
No chloroplasts - no sunlight = no need for chloroplasts because it cannot photosynthesise.
Investigate, using a suitable stain, the pathway of water through the above-ground parts of a plant.
Food dye.
Define transpiration
Evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through the stomata.
The movement of water molecules through the plant. Up from the roots, through the xylem vessels and evaporating out through the stomata in the leaves.
Describe the effects of variation of temperature, humidity and light intensity on transpiration rate.
Light intensity
Light intensity up = transpiration up
More light = more photosynthesis therefore more water used.
The stomata open wider to allow more CO2 into the leaf for photosynthesis.
Temperature
Temperature up = transpiration up
Higher temperature = more evaporation therefore more transpiration.
Evaporation and diffusion are faster at higher temperature.
Wind
Wind up = Transpiration up
More diffusion therefore more transpiration. Water vapour removed quickly by air movement, speeding up the diffusion of more vapour out of the leaf.
Humidity
Humidity up = transpiration down.
Less diffusion therefore less transpiration. Concentration gradient is smaller. Leaf is already surrounded by moist air.
The rate of transpiration is determined by the limiting factor. This is the component of transpiration which is the “least”. If this limiting factor is increased then the rate of photosynthesis will increase until another factor limits the rate.
Define hormone
A chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver.
State the role of the hormone adrenaline in chemical control of metabolic activity
- increasing blood glucose concentration and pulse rate
- produced in the adrenal gland
- decreases reaction times
- increases breathing rate
- diverts blood to muscles (away from eg digestive system)
- hairs stand up
- generated in nervous or frightening situations.
Give examples of situations in which adrenaline secretion increases
Fight or flight situations, stage fright.
Define and investigate GEOTROPISM and PHOTOTROPISM
Geotropism - growth in response to the direction of GRAVITY.
Positive geotropism at root tip - grows towards gravity - more chance of finding moisture.
Negative geotropism at stem tip - grows away from gravity - more chance of finding light.
Phototropism - growth in response to the direction of LIGHT
Positive phototropism at stem tip - growth towards light to get maximum light for photosynthesis.
Negative phototropism at root tip - growth away from light - less chance of drying out.
Explain the chemical control of plant growth by auxins including geotropism and phototropism in terms of auxins regulating differential growth.
Auxin: a plant hormone responsible for controlling the direction of growth of root tips and stem tips in response to different stimuli including light and gravity.
It is made the the tips of stems and roots. It controls the rate of plant growth.
Phototropism - auxin production on the side opposite to light to make that side grow faster to face the sun.
In a shoot, the side containing auxin grows faster, however in the roots, the shaded side contains more auxins, but this side grows slower, bending the root away from light.
Geotropism - auxins production on the bottom side, this causes the root grow less on the bottom side, bending in the direction of the force of gravity.
In a horizontal shoot, the bottom side contains more auxins than the top, This makes the bottom side grow more than the top side, causing the shoot to bend against the direction of gravity.
Auxins are always placed in the shadiest side, this is because the side with the sun destroys the auxin in that side of the plant.
Define asexual reproduction
The process resulting in the production of genetically identical offspring from one parent.
- fertilisation not involved.
- no male/female
- splitting of a cell
- gametes not involved
- used by plants
Define sexual reproduction
The process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring.
- gametes involved
- used by mammals
- often two parents, sometimes only one
- fertilisation involved
- young genetically different from each other, and from parent or parents.
Haploid = 23 chromosomes Diploid = 23 PAIRS after fertilisation Zygote = fertilised cell
Each diploid cell contains 2 copies of each chromosomes - one from the mother, one from the father.
Identify and draw the sepals, petals, stamens, anthers, carpels, ovaries and stigmas of a insect pollinated flower.
Draw and label.
State the functions of the sepals, petals, anthers, stigmas and ovaries.
Sepal: Leaf-like structure at flower base, protects young flower bud
Petals: Located in and above the sepals, often large and colourful, sometimes scented, sometimes producing nectar. Often serve to attract pollinators to the plant.
Anthers: Structure which produces pollen grains
Stigma: sticky top of carpel/style, serves as a receptive surface for pollen grains.
Ovaries: enlarged base of the carpel containing the ovule(s). The ovary matures to become a fruit.