4. PLANT HORMONES- Plants are sensitive to light, moisture and gravity. Their shoots grow towards the light and against the force of gravity. Their roots grow towards moisture and in the direction of the force of gravity. Plants produce hormones that co-ordinate and control this growth. They are known as AUXINS.
Auxins (plant hormones) affect the growth of plants in the following ways:
- Cause shoot growth by cell elongation
- Prevent side branching
Auxins are used commercially for the following uses:
- To kill weeds by disrupting their normal growth
- To reproduce large numbers of plants quickly by stimulating the growth of roots from cuttings
- To regulate the ripening of fruits on the plant and during transport to customers
5. TRANSPORT IN PLANTS - the transportation of water is vital in plants. A lack of water will lead to wilting and the eventual death of the plant.
HOW DO WATER AND MINERALS ENTER A PLANT?
* Root hair cells absorb water by osmosis.
* Minerals are absorbed by diffusion or active transport.
* Water and soluble minerals are transported in xylem vessels. Soluble food substances eg. Glucose is transported in phloem tubes.
HOW DOES WATER LEAVE A PLANT?
Plants lose water vapour from the surface of their leaves. This loss of water is known as transpiration. Transpiration is the process by which water evaporates from the leaf through the stomata creating a pull causing water to rise up the plant in the transpiration stream. The size of stomata is controlled by guard cells, which surround them. If plants lose water faster than the roots replace it, the stomata can close to prevent wilting. Transpiration is more rapid in hot, dry and windy conditions. Most plants have a waxy layer (cuticle) on their leaves, which stops them losing too much water. Plants living in dry conditions have a thicker cuticle.
HOW IS WATER TRANSPOPRTED WITHIN A PLANT?
- XYLEM TISSUE – transport water and minerals from the roots to the leaves.
HOW ARE NUTRIENTS TRANSPORTED?
- PHLOEM TISSUE – transports sugars from the leaves to the rest of the plant.
- HOW DO SUBSTANCES ENTER AND LEAVE CELLS?
DIFFUSION – ‘movement of particles from a region of high concentration to a region of low concentration’.
OSMOSIS – ‘movement of water particles from a region of high concentration to a region of low concentration across a partially permeable membrane’.
ACTIVE TRANSPORT – ‘an energy requiring process by which cells take substances against a concentration gradient’. This enables plants to absorb mineral ions from very dilute solutions.
7. CENTRAL NERVOUS SYSTEM – The Central nervous system consists of the brain and spinal cord. A network of nerves connects the brain and spinal cord to the body. Messages travel throughout the nervous system via nerve impulses. Nerve impulses are electrical impulses.
SENSE ORGANS, RECEPTORS and STIMULI
REFLEX ACTIONS - an automatic response to a stimulus.
REFLEX ARC - the route taken by a nerve impulse through the nervous system. A reflex arc consists of three parts:
- Sensory neurone - carrying a nerve impulse from a receptor to the spinal cord or brain.
- Relay neurone - carrying the impulse through the spinal cord.
- Effector/Motor neurone - carrying the impulse from the spinal cord to the effector.
SYNAPSE - a gap between neurones. A chemical is released at a synapse allowing the passage of the impulse across the synapse.
8. THE EYE- identify and explain the function of each eye part:
*Sclera – tough white protective layer
*Cornea - focusing.
*Lens - focusing.
*Iris - controls the amount of light reaching the retina through the pupil.
*Retina - light sensitive layer containing light receptors.
*Optic Nerve - carrying impulses from the retina to the brain.
Light from an object enters the eye through the cornea. The curved cornea and lens help to focus an image onto the retina. The receptor cells in the retina send impulses to the brain along sensory neurones in the optic nerve.
The shape of the lens can be altered, by contraction or relaxation of the ciliary muscles, to focus near or distant objects respectively. Electrical impulses transmit information from receptor cells along sensory neurones to the central nervous system that includes the brain and spinal cord.
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HOMEOSTASIS (the maintenance of a relatively constant internal environment)
- Maintenance of body temperature
- Maintenance of body water content
- Maintenance of blood glucose levels
- Maintenance of ion content of the body
- ROLE of the SKIN
- A waterproof and germ-proof layer
- Temperature control by sweating and by changes in the diameter of the skin’s superficial capillaries.
11. THE EXCRETORY SYSTEM (maintaining water balance and removing waste).
You must appreciate the role of the kidneys - to remove unwanted substances from the blood and pass them onto the bladder to be excreted.
Identify and recall the function of:
- Kidneys - filtration and reabsorption.
- Renal artery - carries ‘dirty blood’ to the kidney.
- Renal vein - carries ‘clean blood’ away from the kidney.
- Ureters - transport urine to the bladder.
- Bladder - stores urine.
- Urethra - transports urine out of the body.
NEPHRON - each kidney consists of approximately 1million nephrons. You must be able to identify the following nephron parts:
- Glomerulus - dense capillary network
- Renal capsule (Bowman’s capsule) - a cup-like structure holding the glomerulus
- Renal tubule and associated blood capillaries
- Collecting duct - where urine collects
HOW THE NEPHRON WORKS - PART 1 - PRESSURE FILTRATION
- ‘Dirty blood’ is carried to the nephron by the renal artery to the glomerulus.
- Blood enters the glomerulus at high pressure. This causes water, nutrients, salts and urea to pass into the Bowman’s capsule. This mixture is known as the filtrate.
HOW THE NEPHRON WORKS - PART 2 - REABSORPTION
- Some water and salts from the filtrate passes back into the blood. All glucose is reabsorbed.
- Urea, excess water and salts flows to the collecting duct.
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Collecting Duct → Ureter → Bladder → Urethra → Toilet!!
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NEGATIVE FEEDBACK - response reduces the strength of the original stimulus.
Example 1. Temperature Control
STIMULUS (increase in temperature)
RECEPTOR
RESPONSE BRAIN decrease in temperature
EFFECTOR
sweating/ capillaries dilate
Example 2. Water Control
STIMULUS (increased water in the blood)
RECEPTOR
RESPONSE BRAIN decreased water in the
blood
EFFECTOR
less ADH secreted
ADH - ANTI -DIURETIC HORMONE - causes the kidneys to absorb more water
Example 3. Glucose Control
STIMULUS (increased glucose in the blood)
RECEPTOR
RESPONSE BRAIN decreased glucose in the
blood
EFFECTOR
more insulin
secreted
INSULIN - removes glucose from the blood and stores it as glycogen in the liver.
13. DRUGS (substances which alters the way the body works)
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Tobacco Smoking- contains harmul chemicals e.g,
-Tar deposits in the lungs and causes cancer.
-Nicotine (the addictive part) causes constriction of blood vessels and makes the hard beat faster.
-Carbon monoxide prevents haemoglobin from carrying as much oxygen.
Carbon monoxide combines irreversibly with the haemoglobin in red blood cells
SMOKING DURING PREGNANCY INCREASES THE CHANCES OF DISABILITY AND PREMATURE LABOUR. THE FOETUS IS DEPRIVED OF OXYGEN LEADING TO A LOW BIRTH WEIGHT.
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Alcohol Abuse - causes impairment of judgement, slowing down reactions and possible damage to brain and liver cells.
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Solvent Abuse - causes hallucinations and damage to lungs, liver and brain..
ADDICTION - drug use may lead to addiction. This is a state in which the body can not function normally without the drug and a person may suffer withdrawal symptoms without them.
