• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Auxins: Plant growth Hormones.

Extracts from this document...

Introduction

Biology Revision Notes Auxins: Plant growth Hormones Auxins are hormones and are "chemical messengers" The have many roles in plants including: 1. Growth of cells by cell elongation 2. Prevention of side shoot development Growth of cells The auxin in the cells makes the cells stretchy and this is called cell elongation without it the cell would just continue to multiply Auxins allow the cellulose cell walls of young plant cells to become stretchy Because the cells contain sugars and salts, they will take up water (by osmosis) and expand. Light influences the movement of Auxin within a plant i.e. the Auxin MOVES AWAY FROM THE LIGHT. This causes the pants to grow towards the light The reason that it does this is because the auxin elongates the cells on the side that it is on (the side opposite the light) and elongates the cells making the plant longer on one side so naturally the plants bends towards the light Summary * Auxin causes cell elongation and hence growth * Auxin is produced in the tip of a shoot * Auxin is a water soluble chemical which can be absorbed into agar Prevention of side shoot development The apical bud is the source of Auxin .If the bud is present it will prevent side shoot development =Apical dominance This means that it is a tall plant to out compete all other plants for light. ...read more.

Middle

2. The have stomata controlled by guard cells which allow the diffusion of gases into and out of the leaf. 3. Most of the chlorophyll is packed into chloroplasts in the palisade cells which are just below the upper epidermis for maximum light absorption. Action of the guard cell In the light when the plant is photosynthesising, it produces Glucose which increases the concentration of the cell sap and causes it to absorb water by osmosis. This increases the pressure in the guard cells and causes them to stretch and bend, thus opening the stoma. In the inflated state , the cells are said to be Turgid In the dark , photosynthesis stops producing glucose, and the glucose already present is used up by respiration. The guard cells may lose some water by osmosis to the surrounding cells , so they become limp or flaccid. This is the equation for photosynthesis: Light energy Carbon dioxide + water glucose + oxygen Chlorophyll Limiting factors of photosynthesis The rate at which photosynthesis occurs is limited by the following factors: 1. Water- this has and an indirect affect. Lack of water causes the stoma to close and this reduces the amount of carbon dioxide the leaves can absorb Extreme water shortage kills the plant. 2. Carbon dioxide- increasing the carbon dioxide levels leads to increased photosynthesis up to a certain point after which further increase in carbon dioxide levels has no beneficial effect. ...read more.

Conclusion

Regulates the amount of light going into the eye. BLINDSPOT/OPTIC NERVES: the optic nerve leaves the eye at the blind spot and carries all of the sensory nerves to the brain FOVEA; part of the retina opposite the lens with the highest concentration of light receptors for the most detailed images. The heart Arteries :carry blood to tissues Veins: carry it back to the heart Capillaries: allow exchange of chemicals with tissues e.g. glucose + O2 Artery - Carrie sblood away from the heart - blood is under high pressure - therefore they have a tough outer coat to prevent damage - Elastic fibres to smooth out pressure - Circular in cross section Veins - Blood towards heart - under low pressure - Valves to prevent back flow - Irregular in cross section Capillary - the vessels in which chemicals are carries in blood stream are exchanged with living tissue - Link arteries to veins - One cell thick - to speed up diffusion - No valves Blood 1. Red blood cells * Shape inportant- the shape of the red blood celss have a large surface area for maximum uptake of oxygen * RBC's filled with heamoglobin( even the nucleus is excluded to make more room) Heamoglobin (hb) reacts with oxygen but can but can give up that oxygen in the tissues whereit is being usedup i.e. Lungs Hb +o2 Hbo2 Tissues Oxy heamoglobin ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Green Plants as Organisms section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Green Plants as Organisms essays

  1. Marked by a teacher

    An investigation into the effect of a germination inhibitor on the germination of seeds.

    3 star(s)

    And this is also why 10 seeds and 10 concentrations are to be used because this is enough data to carry out the statistical test. Statistical Test This is the section of the investigation where the statistical test is to be used; in this case the test is Chi-squared.

  2. The investigation is aiming to look at transpiration.

    bag 5 0.3 0.3 1.0 0.8 0.7+0.5/2 =0.6 0.6/5 = 0.12 Radiator 5 1.3 1.0 2.1 2.0 0.8+1.0/2 = 0.9 0.9/5 = 0.18 Blocking with Vaseline 5 0.5 0.0 1.0 0.6 0.5+0.6/2 = 0.55 0.55/5 = 0.11 Cutting of leaves 5 2.9 0.0 3.7 0.5 0.8+0.5 =0.65 0.65/5 = 0.13

  1. Discuss the various adaptations of vertebrates that enable them to live in marine conditions.

    Also the presence of blubber in marine mammals contributes to the overall density as well as playing a role in insulation. A final note is that Odobenidae (walruses) have two large air pouches extending from the pharynx which can be inflated to act like a life preserver to keep the animals head above water whilst sleeping.

  2. Experiment to Compare Stomata Density in Different Dicotyledonous

    This plant has a waxy upper epidermis cuticle. Geographic Origin is South Korea, Japan. This plant enjoys full sun to light, dappled shade and moist but well drained soil. The temperature in South Korea ranges from 5-24 degrees whilst the average rain fall in one year is 1425mm.

  1. Design and Carry out an investigation to see what effect light intensity has on ...

    highlighted by the way in which the experiment is to be carried out, the method. Apparatus * Potometer and meter rule * One leafy plant with a suitable size shoot * Beaker of water to fill the reservoir of the potometer * Clamp stands (to support the plant)

  2. Investigating the growth of Lemna (Duckweed)

    It is also applied to form cytochrome, which is an enzyme required for cell respiration. Cytochrome is a group of hemoprotein cell components that, by readily undergoing reduction and oxidation (gain and loss of electrons) with the aid of enzymes, serve a vital function in the transfer of energy within cells.

  1. The effects of organic effluent from the seweage on the biodiversty in a freshwater ...

    This analysis is appropriate whenever you want to compare the means of two groups, and especially appropriate as the analysis for the posttest-only two-group randomized experimental design. Figure 1. Idealized distributions for treated and comparison group posttest values. Figure 1 shows the distributions for the treated (blue) and control (green)

  2. How temperature affects the rate of photosynthesis.

    between enzyme and substrate molecules (and between the other enzyme independent reactant molecules). All the active sites of the enzymes (in both the dark and the light stage) are full and the maximum amount of product is being released at the highest possible rate.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work