This page contains the detailed and easy notes for AQA GCSE Biology Cell Biology for revision and understanding Cell Biology.

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New (9-1) AQA GCSE Biology Paper 2: Complete Revision Summary

HOMEOSTASIS AND RESPONSE

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4.5 Homeostasis and Response  

• Homeostasis
• Human Nervous System
• The Brain
• The Eye
• Thermoregulation
• Endocrine System
• Control of Blood Glucose
• Osmoregulation
• Human Reproduction
• Contraception
• Negative Feedback
• Plant Hormones

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HOMEOSTASIS – The process of maintaining the constant internal environment

Nervous System and the Hormonal System

Homeostasis is important for the enzymes as the enzymes control all the reactions of the body and they need optimum condition to work.

NEURONES

Motor Neurone

• Motor Neurones connect the CNS to the Effectors
• Takes impulses away from CNS
• Motor neurones sends the message from the central nervous system to the effectors.

Sensory Neurone

• Sensory Neurones connect sense organs with the Central Nervous System.

Relay Neurone

• Relay Neurones are present in the CNS and occur between the sensory and motor neurons for distant transmission of Impulses.
• Found in CNS
• Connect Sensory and Motor Neurones

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REFLEX ACTIONS

• It is the automatic response of the body to a stimulus.
• In reflex action the message from the sensory neurones is passed to the spinal chord instead of brain.
• Spinal Chord sends the message to the effectors and produce a response

Example: Knee Jerk Reflexes,

• Touching hot object, Sudden closure of light with bright light
• It is rapid
• It is quick Automatic, Instantaneous without conscious thoughts

Stimulus

Receptor

Spinal Chord

Motor neurones

Effector

Response

SYNAPSE

Message is transmitted by chemicals

BRAIN – It is the Central information processing organ of our body, and acts as the command and Control System.

CEREBRUM (Cerebral Hemisphere) – It is nearly 80% part of the brain

• Consciousness
• Memory
• Intelligence
• Language

CEREBELLUM – It lies behind the cerebrum and above the medulla oblongata. It is the second largest part of brain and is highly convoluted area which accommodates many neurons.

• Muscle Coordination
• Balance

MEDULLA OBLONGATA or oblong marrow is oblong cylindrical part of the brain. It forms the hindermost part of the brain.

• Unconscious Activities like Heart Rate, Breathing.
• Gut Movement

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BRAIN SCAN

Magnetic Resonance Imaging (MRI) helps to take the Images of different parts of the brain and relating it with loss of functions of the individual

Problems

• Brain is complex
• Skull protects the brain
• Thousands and neurones and neurotransmitter are involved
• The functions of different parts is still not understood.
• Drugs do not reach the brain

Homeostasis and Response__ (2)

Eye – It is lodged in orbit of skull, hollow, spherical organ, about 2.5 cm in diameter and about 6-8gram in weight

ACCOMMODATION- Ability of eye to adjust the focal length of the lens to make clear image of the objects lying at varying distances. It is a reflex mechanism and is done with the help of ciliary muscles and suspensory ligament.

For distant vision, ciliary muscle relax making the suspensory ligaments tensed which inturn make the lens thin so that the image is focussed on the retina.

For near vision, ciliary muscle contract making the suspensory ligaments to slack which inturn make the lens thick so that the image is focussed on the retina.

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DEFECTS OF VISION

MYOPIA

• Short sightedness
• The image falls in front of the retina of the eye.
• Eye ball gets elongated
• corrected by concave lens

HYPERMETROPIA

• Long sightedness
• The image falls behind the retina of the eye.
• Eye balls gets shortened
• corrected by convex lens

NEW EYE TECHNOLOGIES

Contact Lenses

• Lenses are placed on the surface of the eye.
• Includes soft, silk and disposable lenses
• Can be used by any person at any age

Laser Surgery

• Laser is used to change the thickness or the curve of the cornea so that defects of vision can be corrected.
• Can be done on adults after the growing age.

Replacement Lens

• It involves either replacing the faulty lens or inserting the correct one with the faulty one.
• Include damage risk to the eye.

HORMONAL CONTROL

HORMONAL and NERVOUS SYSTEM

Hormones

• They are chemical messenger secreted by the endocrine glands
• they are secreted in the blood and travel to the target organ
• Target organ has receptors and hormones
• bind to the receptor and triggers a response
• It produces a slower but long term response

Nervous System

• Is the system of neurones which send electrical impulses to produce a response
• The message is transmitted via electrical impulses
• The response produced is localised and impulses do not travel large distances
• It produces quick but short term response

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PITUITARY : THE MASTER GLAND – Smallest endocrine gland of the body. It is pea shaped, ovoid, reddish brown gland situated at base of the brain in cavity, sella turcica of sphenoid bone. It controls almost all endocrine glands. Hence it is also called master gland

• Master Gland
• It controls other glands of the body
• Follicle Stimulating Hormone
• Antidiuretic Hormone
• Thyroid Stimulating Hormones

EXAMPLES

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CONTROL OF BLOOD GLUCOSE

• Pancreas Insulin and Glucagon (lowers the blood glucose level)
• Increases the blood glucose level)
• Insulin Effect
• It increases the permeability of cells to glucose
• It converts excess glucose to -glycogen
• It converts excess glucose to fats
• It stops the breakdown of fats

Glucagon ‘is the hormone

Glycogen is the stored carbohydrate

DIABETES

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DIABETES TREATMENT

TYPE 1

• Insulin injections directly into the blood stream.
• Less taken orally as being a protein hormone it can get digested by stomach.
• The insulin converts excess glucose into glycogen and control the blood glucose level.
• Less intake of carbohydrates.
• Pancreatic Transplant
• Pancreatic Cell Transplant
• Using stem cells to regenerate pancreatic cells.

TYPE 2

• Balanced diet
• Regular Exercise
• Weight Management
• Drug to increase sensitivity of pancreas to insulin
• Insulin injections to increase the concentration of insulin to make them more responsive to insulin.

NEGATIVE FEEDBACK

• When the level of anything rises above optimum like glucose concentration, water concentration or temperature negative feedback decreases it
• When the level of anything decreases below optimum the negative feedback raises it.

FIGHT OR FLIGHT HORMONE

• Stress Hormone
• Increase heart rate
• Increase breathing rate
• Dilate the pupil

Emergency Hormones

• Increase Blood Flow
• Increase the flow of oxygen to the brain
• Divert blood flow away from the gut

 HUMAN REPRODUCTIVE SYSTEM

TESTOSTERONE

Male hormone responsible for secondary sexual characters

OESTROGEN

Female hormone responsible for secondary sexual characters

MENSTURATION CYCLE

 HORMONES OF MENSTURATION

CONTRACEPTION METHODS

Preventing Sperms to reach the egg. Preventing the implantation of the zygote in the uterus.

Barrier Methods: Prevent the sperm to meet the eggs

Hormonal Methods: Prevents the eggs to mature or prevent the implantation of eggs in the uterus.

Chemical Methods: Kills the sperm

Intrauterine Device: Prevent embryo from implanting

Surgical Method: It is permanent contraception

HOW CONTRACEPTION WORKS?

Contraceptive Pills

• They contain the mix of female hormones oestrogen and progesterone. -MIX PILL
• Prevent the release of FSH preventing the maturation of eggs
• Make thick mucus in the cervix to prevent the entry of sperms.
• Prevent the uterus linning development, preventing implantation.
• Some pills are progesterone only pills.
• A contraceptive implant is also inserted which slowly release progesterone in the uterus.
• A contraceptive patch also absorbs the mix of hormones into the blood
• Side Effects: blood pressure, has to be taken daily changes in menstural pattern

Contraceptive Pills

• They contain the mix of female hormones oestrogen and progesterone. -MIX PILL
• Prevent the release of FSH preventing the maturation of eggs
• Make thick mucus in the cervix to prevent the entry of sperms.
• Prevent the uterus linning development, preventing implantation.
• Some pills are progesterone only pills.
• A contraceptive implant is also inserted which slowly release progesterone in the uterus.
• A contraceptive patch also absorbs the mix of hormones into the blood
• Side Effects: blood pressure, has to be taken daily changes in menstural pattern

Intra Uterine Device

• Copper T is inserted into the uterus
• It releases copper ions which are toxic to sperms
• The device also prevent the implanting of the embryo into the uterus
• Some releases progesterones which works the same like contraceptive pills
• Prevent the release of FSH preventing the maturation of eggs
• Make thick mucus in the cervix to prevent the entry of sperms.
• Prevent the uterus linning development, preventing implantatiom
• Side Effects: Infection; Internal Bleeding

 Surgical Methods

VASECTOMY: Male Sterlization

• Sperms ducts are cut and sealed so that the sperms cannot enter the urethra preventing fertilization.

TUBECTOMY: Femal Sterlization

• The oviducts are cut and tied to prevent the release of egg which prevent
• Sterlizatlom
• Side Effects – It is permanent.

INFERTILITY PROBLEMS

OVULATION PROBLEM

• The eggs do not mature or problem ovulating.
• The women is given fertility drugs which are the mix of FSH and LH that stimulated maturation and ovulation

FAULTY TUBES

IMPLANTATION

• In Vitro Fertilization where fertilization is performed in the laboratory and the embryo is implanted back in the uterus for the development

PREGNANCY DEVELOPMENT

• Surrogate Mother where the fertilized egg is implanted into another mother who gives birth

IN VITRO FERTILIZATION

• Expensive
• Results in multiple embryos
• Premature births
• Birth with disability
• Not always successful

Fertility drugs to stimulate ovulation

Ovary and sperm are collected to perform fertilization.

Fertilized egg is developed in the laboratory giving suitable conditions to develop into an embryo.

Embryo is inserted into the uterus

Develops into a baby.

Plant Hormones

Auxin is produced in the shoot tip. When light falls on auxin it is displaced to the shader side promoting growth of the shader region resulting in growth of shoot towards light.

Gravitropism – The movement of roots towards gravity.

• It is also caused by auxin. In roots auxin inhibits the growth of the roots at the lower side resulting in bending of the root downwards.
• Auxin is displaced to lower side in response to gravity.

PLANT HORMONES

AUXINS

• It stimulates cell divsion and growth of the plant
• It is used to stimulate rooting in tissue culture.
• Used as Weedicide causing excess growth of the weed and killing them.

GIBBERLINS

• Seed germination
• Promote flowering
• End seed dormancy
• Elongation of stem.

ETHENE

• It is a gaseous hormone
• It is involved in fruit ripening
• Allows transportation of raw fruit to long distances and then they can be ripped by ethene.

Cytokinin

Caused Cell Division

Abscicic acid

Stress hormone prepared the plant for stress conditions

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WASTE PRODUCTS

The products produced during metabolic reactions like respiration, digestion etc.

Carbon Dioxide

• Produced during respiration.
• Is excreted out through the lungs by the process of expiration
• Carbon dioxide is harmful as it can alter the pH of the blood affecting enzyme activity.

Water

• Produced during respiration and digestion process.
• Is excreted through skin in the forms of sweating or some by breathing and by kidney in the form of urine.
• Water can also disturb the osmotic balance and salt level of the body.

Urea

• Produced by the liver by metabolising excress proteins as it is toxic and cannot be stored.
• It is excreted by Kidney in the form of Urine.

HUMAN EXCRETORY SYSTEM

ULTRAFILTRATION

• Kidneys filters the blood at a very high pressure.
• All the water, glucose, and useful components gets into the kidney filtrate. The blood cells and blood proteins due to their bigger Size are not filtered.

SELECTIVE REABSORPTION

• Since the kidney contains useful substance in the filtrate it reabsorbs back them into the blood.
• The water also gets reabsorbed depending on the needs of the body.

 OSMOREGULATION

DIALYSIS

• Artificial Kidney blood flows into the dialysis machine which contains dialysis fluid.
• Dialysis fluid contains the same concentration of essential minerals ions,as that of blood but no urea.
• As blood flows into the dialysis fluid, urea is diffused out along the concentration gradient and excess salt is also removed maintaing the normal salt and mineral ions level.
• The clean blood is then pumped back.
• Lifestyle changes, regular visits, change in diet and regular expenditure are some of the disadvantages.

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KIDNEY TRANSPLANT

• Replacing diseased kidney with the healthy one.
• The donor should be a close relative to prevent rejection.
• The person has to be on Immuno – suprresant drugs so that the body immune system does not reject it.
• Does not last long and person is prone to other infectious diseases due to immuno suppresant drugs.

DIALYSIS KIDNEY TRANSPLANT

DIALYSIS

Advantages

• No surgery
• No infection
• No immuno supressant drugs
• Easyily available

Disadvantages

• Lifestyle changes
• Regular visits and long procedure
• Restricted Diet

KIDNEY TRANSPLANT

Advantages

• No regular visit
• No lifestyle changes
• No diet restriction

Disadvantages

• Does not last forever
• Chances of rejection
• Immuno supressant drugs to be taken
• Person is more prone to infections.
• Finding a suitable donor is a problem

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KEY TERMS

• Homeostasis – Homeostasis is the process of an organism to maintain a stable internal environment adequate to sustain life.
• Receptors – Receptor is any cell or organ of an animal capable of detecting a stimulus is a change in the external or internal environment and which subsequently brings about a response in the behavior of the animal.
• Effectors – Effector is any muscle, gland or an organ capable of responding to a stimulus, particularly a nervous impulse.
• Stimulus – A biological stimulus is any external change in the environment that can be detected by an organism.
• Neurones – These are structural and functional Units of Neural System. Each Neuron consists of the cell body (cyton) and nerve fibre (axon)
• Central Nervous System – Consists of Brain and Spinal cord
• Sensory Neurones – These connect sense organs with the Central Nervous System.
• Motor Neurones – These connect the CNS to the Effectors
• Relay Neurones – These are present in the CNS and occur between the sensory and motor neurons for distant transmission of Impulses.
• Reflex Arc – The path followed by the stimulus (impulse) from beginning to end is the reflected arc.
• Brain – It is the Central information processing organ of our body, and acts as the command and Control System.
• Cerebral Cortex – Grey matter forms 2-4mm thick outer cortex of cerebrum called cerebral cortex
• Cerebellum – literally means little cerebrum. Cerebellum has grey matter on outer side and made of three layers of cells and fibres. 2^nd largest part of the brain.
• Medulla – directly controls some ANS responses, such as heart rate, respiration, dilation of blood vessels, digestion, sneezing, swallowing and vomiting. It is a part of the brain stem, located just below the prominence and just above the spinal cord.
• Magnetic Resonance Imaging (MRI) – It helps to take the Images of different parts of the brain and relating it with loss of functions of the individual
• Eye – Hollow spherical organ, about 2.5cm in diameter and about 6-8gm in weight. It is lodged in orbit of skull.
• Blind Spot – The spot on the retina which has no receptor.
• Accomodation- Ability of eye to adjust the focal length of the lens to make clear image of the objects lying at varying distances. It is a reflex mechanism and is done with the help of ciliary muscles and suspensory ligament.
• Ciliary Muscles – help in accommodation and ciliary process that secrets aqueous humour.
• Iris – Visible coloured portion of the eye, contains two types of muscles- circular and radial.
• Pupil – In front of the lens the aperture surrounded by the iris is called the pupil.
• Myopia – Also known as near sightness or short sightness. Near object is Clear. Far object is not clear. Eyeball become longer.
• Hypermetropia – long sightness. Far object is clear, near object is not Clear. Eyeball becomes short.
• Endocrine System – the endocrine system consists of glands widely separated from each other with no direct anatomical links. Also called ductless glands
• Hormones – Hormones are the chemical substances produced in the body that controls and regulates the activity of some cells or organs.
• Adrenaline – It is a hormone released by the adrenal glands and its main action, along with norepinephrine, is to prepare the body to “fight or flee”.
• Insulin – Secreted by Pancreas, is a small protein whose molecule consists of two polypeptide chains
• Pituitary Gland – Smallest endocrine gland of the body. It is Pea shaped, ovoid, reddish brown gland situated at base of the brain. It controls almost all endocrine glands. Hence it is also called master gland.
• FSH – Follicle Stimulating Hormone. In males stimulates spermatogenesis. In females growth of ovarian follicles upto ovulation.
• Oestrogen – stimulation of growth and activities of female secondary sex organs, development of growing ovarian follicles, mammary gland development.
• Progesterone – it acts on the mammary glands and stimulates the formation of alveoli, milk secretion and supports pregnancy.
• Glucagon – Glucagon is produced to maintain blood glucose levels during fasting and to increase very low glucose levels.
• Glycogen – Glycogen is the major carbohydrate storage form in animals, and corresponds to starch in plants.
• Diabetes – Diabetes is a disease in which your blood glucose, or blood sugar, levels are too high.
• Mensturation – Menstruation or your period is the shedding of the uterine lining once a month.
• Ovulation – the release of an egg from an ovary — occurs about midway through the menstrual cycle.
• Phototropism – It is the ability of a plant, or other photosynthesizing organism, to grow directionally in response to a light source.
• Gravitotropism – Gravitropism is a plant’s natural growth response to the effects of gravity.
• Auxins – Auxin is involved in cell growth and cell expansion
• Gibberlins – Gibberellins promote stem elongation between nodes on the stem.
• Dialysis – The process of removing waste products and excess fluid from the body.
• Selective Reabsorption – Selective reabsorption is the process by which some molecules (eg – Ions, glucose and amino acids), after having been filtered by capillaries together with nitrogen waste products (eg Urea) and water in the glomerulus, are reabsorbed by filtration as they pass through the nephron.

Make sure you have watched the above videos and are familiar with the key definitions before trying these questions. It is also good to time yourself while doing these questions so that you can work on the speed as well

B10-Human Nervous System

• Human Nervous System 1 MS
• Human Nervous System 1 QP
• Human Nervous System 2 MS
• Human Nervous System 2 QP
• Human Nervous System 3 MS
• Human Nervous System 3 QP

B11- Hormonal Coordination In Humans