
- 1 Double-stranded molecule
- 2 Contains the nitrogenous base thymine (T) instead of uracil (U)
- 3 A always joins with T
- 4 G always joins with C
How to recognise a DNA molecule
- 1 Single-stranded molecul
- 2 Contains the nitrogenous base uracil (U) instead of thymine (T)
How to recognise an RNA molecule

- 1 The double helix unwinds.
- 2 Weak hydrogen bonds between nitrogenous bases break and two DNA strands unzip (separate).
- 3 Each original DNA strand serves as a template on which its complement is built.
- 4 Free nucleotides build a DNA strand onto each of the original two DNA strands by attaching to their complementary nitrogenous bases (A to T and C to G).
- 5 This results in two identical dNA molecules. Each molecule consists of one original strand and one new strand.

- Chromosomes shorten and become visible as two chromatids joined by a centromere.
- Homologous pairs of chromosomes are now visible.
- The nuclear membrane and nucleolus disappear.
- The spindle starts to form.
- Chromatids from each homologous pair touch. The point where they touch is called a chiasma.
- DNA is crossed over (swopped) at the chiasma.
- The spindle continues to form.
Metaphase 1
- The spindle extends across the whole cell.
- The homologous chromosomes line up along the equator of the spindle in their homologous pairs.
- One chromosome of each pair lies on either side of the equator.
- The centromere of each chromosome attaches to the spindle fibres.
Anaphase 1
- The spindle fibres shorten and pull each chromosome of each chromosome pair to opposite poles of the cell.
Telophase 1
- The chromosomes reach the poles of the cell.
- Each pole has half the number of chromosomes present in the original cell.
- The cell membrane constricts and divides the cytoplasm in half to form two cells.
Prophase 1

Prophase 2
Metaphase 2
Anaphase 2
Telophase 2



- Seminal vesicle: A gland that produces a nutrientrich fluid that that provides energy for the sperm cells
- Cowper’s gland: Produces mucus that helps with the movement of sperm cells
- Scrotum: Skin sac that protects the testes and holds the testes ‘outside’ the body, at a temperature that is 2°C below 37°C. This is the best temperature for the production of sperm
- Prostate gland: Produces an alkaline fluid that neutralises the acids produced in the vagina, which would kill sperm cells
- Sperm duct: Transports sperm from the epididymis to the urethra
- urethra: Transports semen and urine out of the body
- epididymis: Sperm cells mature and are stored here
- testes: Produces sperm cells and the hormone testosterone

- Acrosome: Contains enzymes to digest wall of egg cell for fertilisation
- Nucleus: Contains 23 chromosomes
- Mitochondria: Provide energy for swimming
- Tail: Used for swimming

- Fallopian tube: Connects the ovaries to the uterus, transports egg cells from the ovary; it is the site of fertilisation
- Ovary: Produces egg cells, secretes progesterone and oestrogen
- Vagina: Receives the penis and semen during sexual intercourse; it is the passage through which the baby is born
- uterus: Carries the embryo and foetus during pregnancy
- endometrium: Inner lining of uterus; place where the embryo implants and the placenta forms
- Cervix: Lower, narrow part of uterus. It stretches to allow the baby through during childbirth


- Ovaries: Mature Graafian follicle develops:
- The Graafian follicle moves to edge of the ovary
- It secretes oestrogen uterus: Oestrogen stimulates the endometrium to become thicker and develop more blood vessels and glands
Day 14
Ovaries: Graafian follicle bursts to release an egg cell.
The process is called ovulation
Day 15–22
Ovaries: The Graafian follicle becomes a corpus luteum that secretes progesterone
uterus: Progesterone stimulates the endometrium to become even thicker and to develop more blood vessels and glands, ready to receive the embryo if an egg cell is fertilised
Day 23–28
Ovaries: If fertilisation does not take place:
- The corpus luteum shrinks and stops secreting progesterone If fertilisation takes place:
- The corpus luteum remains active in the ovary and continues to secrete progesterone
- No more follicles develop in the ovaries
- No menstruation takes place
Day 1–7
Ovaries: New follicles develop and secrete oestrogen
uterus: Lining breaks down and is released (menstruation)
Day 8–13

-
Cerebrum
- Controls voluntary actions
- Receives and interprets sensations from sense organs
- Higher thought processes
- Transmits nerve impulses between the spinal cord and the brain
- Controls involuntary actions such as heartbeat and breathing
- Connects the left and right hemispheres of the brain – allowing communication between both hemispheres
- Control centre for hunger, thirst, sleep, body temperature and emotions
- Coordinates all voluntary movements
- Controls muscle tension to maintain balance

- Motor neuron: Carries the impulse from the spinal cord to the effectors
- Receptor: A structure which receives a stimulus and converts it into an impulse (the heat sensor of the finger feels burn)
- Sensory neuron: Carries the impulse from the receptor to the spinal cord
- effector: A structure which produces the reaction (the muscles in the finger contract and the finger is pulled away)
- interneuron: Carries the impulse from sensory neuron to the motor neuron in the spinal cord
A reflex action is a quick, automatic action that involves the spinal cord and does not involve the brain. It is an important function to protect the body from harm.
The reflex arc is the path along which an impulse is transmitted to bring about a response to a stimulus during a reflex action.


- Dendrite: Transmits impulses towards the cell body of the neuron
- Axon: Transmits impulses away from the cell body of the neuron
Neurons are specialised cells which connect the brain and spinal cord to all other parts of the body.
Sensory (afferent) neuron
Transmits impulses from the sense organs or receptors to the spinal cord and brain.
Motor (efferent) neuron
Transmits impulses from the brain and spinal cord to the effectors (muscles and glands). The effectors bring about the response.
Interneuron (connector)
Links the sensory neuron to the motor neuron.

- Cornea: Responsible for the refraction (bending) of light rays from the object, to create the image on the retina
- Suspensory ligament: Holds the lens in position
- Pupil: A circular opening in the iris which allows light into the eye
- Aqueous humour: Watery fluid that supports the cornea and the front chamber of the eye
- iris: The coloured part of the eye
- Lens: Changes shape for near and distant (far) vision
- Vitreous humour: A jelly-like substance which gives shape to the eye
- Blind spot: This area has no rods and cones; therefore there is no vision at this point
- Optic nerve: Carries nerve impulses from the retina to the brain
- yellow spot: Has the greatest number of cones; this area offers the clearest image
- Choroid: A darkcoloured layer which:
- Reduces reflection
- Is rich in blood vessels which supply the cells of the eye with nutrients and oxygen
- Sclera: The tough white outer coat, which protects the eye against damage
- Retina: Contains the light-sensitive receptor cells, i.e. the rods and cones

- Pinna: Directs sound waves to eardrum
- Oval window: Transmits sound waves to the inner ear
- Round window: Releases pressure from the inner ear
- Tympanum (eardrum): Transmits sound waves to the middle ear
- Ear canal (auditory canal): Transmits sound waves to the eardrum
- Ossicles: Transmit vibrations from the eardrum to inner ear
- Eustachian tube: Equalises pressure on either side of the eardrum
- Semi circular canals: Balance of the body
- Sacculus and utriculus: Balance of the body
- Auditory nerve: Transmits impulses to the brain
- Cochlea: Contains the organ of Corti which converts sound waves into nerve impulses

- Target organ: Kidney
- Controls the concentration of water in the blood
- Controls basic metabolic rate
- heartbeat
- blood pressure
- conversion from glycogen to glucose
- blood supply to the cardiac and skeletal muscles
- skeletal muscle tone
- rate and depth of breathing
- diameter of pupils
Decreases:
- blood flow to the digestive system and skin
- Target organ: Kidney
- Regulates salt concentration in the blood
- Oestrogen – stimulates puberty in females, promotes thickening of the endometrium
- Progesterone – promotes thickening of the endometrium, maintains pregnancy
- Stimulates the maturation of sperm cells
- Stimulates puberty in males
Hypothalamus: ADH (antidiuretic hormone)
Thyroid gland: Thyroxin
Adrenal gland: Adrenalin Increases:
Aldosterone
Ovary (only females):
Reproductive hormones:Oestrogen and progesterone
Testes (only males): Reproductive hormone:
Testosterone
Pancreas: islets of Langerhans
- Stimulates conversion of glycogen to glucose (increases blood glucose levels)
- Stimulates conversion of glucose to glycogen (reduces the blood glucose levels)
Glucagon
Insulin
Pituitary gland (hypophysis):
-
GH (growth hormone)
- Controls growth
- Stimulates thyroid gland to secrete thyroxin
- FSH – stimulates the development of the follicle in the ovaries
- LH – stimulates ovulation, and stimulates development of the corpus luteum
- Prolactin – stimulates the mammary glands to secrete milk
Reproductive hormones:
FSH, LH and prolactin
