STUDY GUIDE TITLE

At a glance: what Paper 1 is

Life Sciences Paper 1 is a 150 mark, 2.5 hour paper written in three sections: Section A (Question 1, 50 marks: multiple choice, biological terminology, matching items and short structured items), Section B (Questions 2 and 3, 40 marks each) and Section C (Question 4, one 20 mark essay).

The content examined in Paper 1 is:

Topic	What it covers
Reproduction in vertebrates	External and internal fertilisation, ovipary, ovovivipary, vivipary, amniotic egg, precocial and altricial development, parental care.
Human reproduction	Male and female reproductive systems, gametogenesis, menstrual cycle, fertilisation, implantation, extra-embryonic membranes, placenta, gestation.
Responding to the environment (humans)	Nervous system, neuron, reflex arc, brain, eye, ear, and their disorders.
Endocrine system and homeostasis	Hormones, negative feedback, thermoregulation, blood glucose, osmoregulation, salt balance.
Responding to the environment (plants)	Auxins, gibberellins, abscisic acid, phototropism, geotropism, and their investigations.

Two topics are guaranteed and are routinely under-taught. The 2025 DBE Diagnostic Report states that reproductive strategies and plant responses to the environment are "a compulsory inclusion in the paper for 8 and 13 marks respectively". That is 21 marks of the 150 that you can bank before you walk in.

What the 2025 examiners actually said about Paper 1

These are the findings from the 2025 NSC Diagnostic Report, Chapter 8. They are the single most useful thing in this guide, because they tell you where marks were lost by candidates who knew the content.

Average performance per question, Paper 1 (2025)

Sub-question	Topic	Average
1.1	MCQ	61%
1.2	Terminology	57%
1.3	Matching items	63%
1.4	Plant growth responses	61%
1.5	Human responses (neurons)	69%
2.1	Reproductive strategies	64%
2.2	Male reproduction	68%
2.3	Menstruation	47%
2.4	Homeostasis, thermoregulation	45%
2.5	Investigation on growth hormone	33%
3.1	Eye defect (astigmatism)	47%
3.2	Brain and spinal cord	54%
3.3	Accommodation (distant vision)	46%
3.4	Hearing and balance	42%
3.5	Investigation on insulin treatment	40%

Read that table again. The five weakest items were the two scientific investigations, thermoregulation, hearing and balance, and accommodation. Nothing there is hard content. It is all higher-order application. The report puts it plainly: "it was not really the content that posed the greatest difficulty, but rather the cognitive demand."

The exact spelling errors that cost marks in 2025

• Evolution instead of ovulation
• Choroid instead of chorion
• Auxin instead of axon
• Multiply sclerosis instead of multiple sclerosis
• Testone instead of testosterone
• Circular instead of ciliary muscles
• Aqueous fluid instead of aqueous humour, and vitreous instead of aqueous

The disorders that were tested in 2025

Cataracts, multiple sclerosis, growth hormone deficiency, astigmatism, hearing loss and diabetes mellitus. The report recommends learning every disorder in this fixed format:

1. Identify the structure.
2. Identify its function.
3. How is the function affected when the structure is damaged?
4. How may the disorder be treated or corrected?

Confusable pairs: the marks you lose to the wrong word

Every pair below comes from an error the 2025 or 2024 Diagnostic Report actually recorded. Drill these until the difference is automatic. The quiz tab tests every one of them.

You wrote	The memo wanted	The difference
Choroid	Chorion	Choroid is the pigmented layer of the eye that absorbs light. Chorion is the outermost extra-embryonic membrane that forms the placenta with the endometrium.
Ovulation, or ovarian cycle	Oogenesis	Oogenesis is the formation of an ovum by meiosis. Ovulation is the single event of releasing that ovum from the Graafian follicle.
Yellow spot	Blind spot	Yellow spot (macula) is the point of sharpest vision, packed with cones. Blind spot is where the optic nerve leaves the eye, no receptors at all.
Pupillary mechanism	Accommodation	Accommodation responds to the distance of an object, using ciliary muscles, changing lens shape. The pupillary mechanism responds to light intensity, using circular and radial muscles, changing pupil diameter.
Circular muscles	Ciliary muscles	Ciliary muscles change lens convexity in accommodation. Circular muscles of the iris constrict the pupil.
Ciliary body	Ciliary muscle	The body is the structure, the muscle is the contractile tissue in it. The memo asks for the muscle.
Suspensory ligaments contract	Suspensory ligaments become taut	Ligaments cannot contract. Only muscles contract. Writing "contract" loses the mark outright.
Maculae	Cristae	Cristae in the semi-circular canals detect a change in speed and direction of movement. Maculae in the utriculus and sacculus detect a change in the position of the head.
Auditory canal	Auditory nerve	The canal conducts sound waves. The nerve conducts impulses to the brain. Do not swap them in the hearing or balance description.
Vitreous humour	Aqueous humour	Aqueous is the watery fluid in front of the lens, between the cornea and the lens. Vitreous is the jelly behind the lens.
Inner ear	Cochlea	Not all of the inner ear is involved in hearing. Name the cochlea when you describe hearing.
Auxin	Axon	Two different words. Auxin is a plant hormone, the axon is part of a neuron.
Alzheimer's disease	Multiple sclerosis	MS is the breakdown of the myelin sheath. Alzheimer's is not.
Cataracts	Astigmatism	Astigmatism is an uneven curvature of the cornea or lens giving distorted vision. A cataract is an opaque lens.
Reflection	Refraction	Refraction is the bending of light as it passes through the cornea and lens. Reflection is light bouncing off a surface.
Less light is refracted	Light is refracted less	The first is about the amount of light. The memo is about the degree of refraction.
Glycogen converted to glucose	Glucose converted to glycogen	Insulin drives glucose to glycogen. Glucagon drives glycogen to glucose. Get the direction right.
Glucagon	Glycogen	Glucagon is the hormone. Glycogen is the storage carbohydrate. One letter, whole mark.
Vasodilation	Vasoconstriction	On a cold day the arterioles constrict so less blood flows to the skin and heat is retained.
Blood flows to the skin	MORE blood flows to the skin	Blood always flows to the skin. The physiological point is the change. Quantify it: more, less, higher, lower.
Central	Central nervous system	The full name is required even when "nervous system" appears in the question.
Spinal cord	Spinal nerve	The dorsal and ventral roots are branches of the spinal nerve, not of the spinal cord.
The stimulus is transmitted	The impulse is transmitted	A stimulus is detected. An impulse is transmitted.
Efferent, unipolar or multipolar neuron	Sensory neuron	Use the CAPS terms: sensory, motor, interneuron.
Umbilical artery	Umbilical vein	The umbilical vein carries oxygen and nutrient rich blood from the placenta to the foetus. The artery carries deoxygenated blood and wastes away from the foetus.
Spermatogonia, spermatocyte, spermatid	Diploid and haploid cells	The old terminology is no longer required. What earns the marks is meiosis, diploid cell, haploid cells.
Maintains pregnancy	Allows implantation, more vascular, more glandular	Too vague loses the mark. Be specific about the endometrium.
Average height, 2 years old	Height, age	A variable is what is measured. Not the description of a step in the method.
Reliability	Validity	Validity is fairness, everything constant except the independent variable. Reliability is repeats, large sample, many measurements. Never mention both when one is asked.
Describe	Explain	Describe is how something happens. Explain is how AND why, in cause and effect.

Reproduction in vertebrates

Fertilisation

	External fertilisation	Internal fertilisation
Where	Outside the female body, in water	Inside the female body
Number of gametes	Very many	Few
Chance of fertilisation	Low	High, gametes are in close contact
Protection	Gametes exposed to predation, currents, drying out	Gametes and zygote protected from predators and the environment
Water needed	Yes	No

Reproductive strategies

• Ovipary: eggs are laid and the embryo develops outside the mother, using yolk as its food.
• Ovovivipary: eggs are retained and hatch inside the female body, the young are born live, but the embryo is fed by the yolk in the egg, not by the mother.
• Vivipary: the embryo develops inside the uterus and is nourished through a placenta and umbilical cord.

The amniotic egg

Structure	Function
Shell	Protects the embryo and prevents it from drying out
Amnion and amniotic fluid	Protects against mechanical injury and prevents drying out
Yolk sac	Stores food for the developing embryo
Allantois	Stores nitrogenous wastes and helps with gaseous exchange
Chorion	Outermost membrane, surrounds everything, allows gaseous exchange

Precocial and altricial development

Precocial	Altricial
Hatch well developed, eyes open, down feathers present	Hatch poorly developed, eyes closed, no down feathers
Can move around and feed soon after hatching	Cannot move, dependent on parents for food and protection
Large yolk in the egg	Small yolk in the egg
Low degree of parental care	High degree of parental care

The 2025 report notes that in the data question on yolk size, candidates quoted a value such as "35,4%" without saying whether it was higher or lower and what that meant. Always: quote the value, say higher or lower, then state the significance.

Human reproduction

Male system

Structure	Function
Testes, seminiferous tubules	Produce sperm by spermatogenesis and secrete testosterone
Scrotum	Holds the testes outside the body cavity so the temperature is about 2 degrees lower, which is required for sperm production
Epididymis	Long coiled tube where sperm mature and are stored
Vas deferens (sperm duct)	Carries sperm from the epididymis to the urethra
Prostate gland	Secretes an alkaline fluid that neutralises the acidic environment of the vagina
Seminal vesicle	Secretes a fluid rich in fructose that provides energy for sperm

Sperm structure

Part	Role
Acrosome	Contains enzymes that digest the outer membrane of the ovum
Nucleus	Carries the haploid genetic material that fuses with the ovum nucleus to form the zygote
Mitochondria	Release energy that enables the tail to move
Tail (flagellum)	Propels the sperm

The menstrual cycle

This is the summary set out in the 2025 Diagnostic Report. Learn it as a chain of causes, not as a list of hormones.

Event	What happens
Increase in FSH	Causes ovarian follicles to develop and mature into a Graafian follicle
Mature Graafian follicle	Secretes oestrogen
Increased oestrogen	Causes the initial thickening of the endometrium
Increase in LH	Brings about ovulation
Corpus luteum forms	Secretes progesterone
Increased progesterone	Causes further thickening of the endometrium, more vascular and more glandular
High progesterone	Inhibits LH secretion (and FSH), this is the negative feedback
No fertilisation	Corpus luteum degenerates, progesterone drops, endometrium is shed as menstruation
Fertilisation occurs	Corpus luteum does not degenerate and keeps secreting progesterone, later the placenta secretes it, so the level stays high

Do not assume ovulation is on day 14. The report warns that the data given in the question may point to a different day. Answer from the resource, not from memory.

From fertilisation to implantation

Zygote, divides by mitosis, to form a solid ball of cells called the morula, which becomes the blastocyst, which develops into the embryo and attaches onto the endometrium (implantation).

Extra-embryonic membranes and the placenta

Structure	Function
Amnion and amniotic fluid	Shock absorber, temperature regulator, prevents dehydration, medium for the foetus to move in
Chorion	Forms chorionic villi that attach to the endometrium, together they form the placenta
Placenta	Exchange of nutrients, oxygen and wastes, and secretes progesterone which further thickens the endometrium
Umbilical vein	Carries oxygenated, nutrient rich blood from the placenta to the foetus
Umbilical artery	Carries deoxygenated blood and wastes from the foetus to the placenta

The nervous system

Divisions

• Central nervous system: brain and spinal cord. Protected by the cranium and vertebral column, the meninges, and cerebrospinal fluid.
• Peripheral nervous system: cranial and spinal nerves. Splits into the somatic system (voluntary) and the autonomic system (involuntary).
• Autonomic: sympathetic speeds things up for an emergency, parasympathetic returns them to normal.

The brain

Part	Function
Cerebrum	Thought, memory, speech, interpretation of all sensations including sound and sight
Cerebellum	Co-ordinates voluntary muscle actions and maintains balance and posture
Medulla oblongata	Controls heart rate, breathing rate, blood pressure and other involuntary actions
Hypothalamus	Controls body temperature, water balance, and links the nervous and endocrine systems
Corpus callosum	Joins the two hemispheres of the cerebrum
Pituitary gland (hypophysis)	An endocrine gland, the master gland

The reflex arc

Stimulus, receptor, sensory neuron, dorsal root of the spinal nerve, interneuron in the spinal cord, ventral root of the spinal nerve, motor neuron, effector, response. There are synapses between the neurons, which ensure that impulses travel in one direction only.

A reflex action is a rapid, automatic response to a stimulus that protects the body from damage.

Multiple sclerosis

The myelin sheath degenerates. The axon is no longer insulated, so the speed of transmission of nerve impulses decreases, which leads to delayed responses and therefore loss of muscle control.

The eye

Part	Function
Cornea	Refracts light entering the eye
Aqueous humour	Watery fluid between the cornea and lens, supports the cornea and the front chamber and refracts light
Iris	Contains circular and radial muscles that change the size of the pupil
Lens	Transparent, biconvex and elastic, refracts light and changes shape to focus
Vitreous humour	Jelly behind the lens, keeps the eyeball in shape and refracts light
Choroid	Contains blood vessels and pigment that absorbs light to prevent internal reflection
Retina	Contains rods and cones, converts light stimuli into impulses
Yellow spot (macula)	Point of sharpest vision, mostly cones
Blind spot	Where the optic nerve leaves the eye, no receptors
Sclera	Tough outer layer, protects the eyeball and gives it shape

Accommodation versus the pupillary mechanism

This is the comparison table given in the 2025 Diagnostic Report.

	Accommodation	Pupillary mechanism
Response to	Distance of object	Light intensity
Response by	Ciliary muscles	Circular and radial muscles
Causes	Lens shape to change	Pupil diameter to change
Affects	Light refraction	Amount of light entering the eye
Results in	Clear image on the retina	Prevention of damage to retina, or clear vision in the dark

Accommodation, the two cases

	Near object (reading a book)	Distant object
Ciliary muscles	Contract	Relax
Suspensory ligaments	Become slack	Become taut
Lens	More convex	Less convex
Refraction	Light is refracted more	Light is refracted less
Result	Clear image focused on the retina	Clear image focused on the retina

Eye disorders

Disorder	Cause	Effect	Correction
Short-sightedness (myopia)	Eyeball too long or lens too convex	Image forms in front of the retina, distant objects blurred	Concave lens
Long-sightedness (hypermetropia)	Eyeball too short or cornea or lens too flat	Image forms behind the retina, near objects blurred	Convex lens
Astigmatism	Uneven curvature of the cornea or lens	Light is refracted unevenly, so a distorted image forms	Cylindrical lens, or corrective surgery
Cataract	Proteins in the lens disintegrate and clump together	Lens becomes opaque, less or no light reaches the retina, so fewer stimuli are converted to impulses	Replace the lens surgically

The ear

Part	Function
Pinna	Directs sound waves into the auditory canal
Auditory canal	Conducts sound waves to the tympanic membrane
Tympanic membrane	Vibrates and transmits the vibrations to the ossicles
Ossicles (malleus, incus, stapes)	Amplify the vibrations and transmit them to the oval window
Eustachian tube	Equalises pressure on either side of the tympanic membrane
Oval window	Transfers vibrations into the cochlea as pressure waves
Round window	Absorbs excess pressure waves from the inner ear, prevents echo
Cochlea	Contains the organ of Corti with receptors for hearing
Semi-circular canals	Contain cristae, detect change in speed and direction of movement
Utriculus and sacculus	Contain maculae, detect change in the position of the head
Auditory nerve	Transmits impulses to the brain

The hearing pathway

The 2025 report gives the mode of transmission across the structures:

SOUND WAVES in the auditory canal, then VIBRATIONS at the tympanum and ossicles, then PRESSURE WAVES in the cochlea, then IMPULSE along the auditory nerve, to the CEREBRUM for interpretation.

Balance, the table the report recommends

Stimulus	Receptor	Transmits impulse	Part of brain	Effector
Change in head position	Maculae	Auditory nerve	Cerebellum	Skeletal muscles
Movement, change in speed and direction	Cristae	Auditory nerve	Cerebellum	Skeletal muscles

The endocrine system

Gland	Hormone	Function
Pituitary (hypophysis)	FSH	Stimulates development of ovarian follicles and initiates puberty, stimulates sperm formation in males
Pituitary	LH	Stimulates ovulation and the development of the corpus luteum
Pituitary	TSH	Stimulates the thyroid to secrete thyroxin
Pituitary	ADH	Increases reabsorption of water in the kidney tubules, osmoregulation
Pituitary	Prolactin	Stimulates the mammary glands to produce milk
Pituitary	Growth hormone	Stimulates growth of bones and muscles
Thyroid	Thyroxin	Regulates metabolic rate, affects growth and functioning of the heart and nervous system, influences bone development
Adrenal	Adrenalin	Prepares the body for an emergency, fight or flight
Adrenal	Aldosterone	Increases reabsorption of salt in the kidney tubules
Pancreas, islets of Langerhans	Insulin	Lowers blood glucose
Pancreas, islets of Langerhans	Glucagon	Raises blood glucose
Testes	Testosterone	Stimulates puberty and the formation of sperm
Ovaries	Oestrogen	Secondary sexual characteristics and initial thickening of the endometrium
Ovaries, corpus luteum	Progesterone	Further thickening of the endometrium and maintenance of pregnancy

Homeostasis

Homeostasis is the maintenance of a constant internal environment within certain limits. It works by negative feedback: a change is detected, a correcting mechanism is set off, and the correction switches off the stimulus.

Thyroxin, the negative feedback loop

The thyroxin level is low, the pituitary gland is stimulated, more TSH is secreted, which stimulates the thyroid gland to secrete more thyroxin. When thyroxin rises above normal, TSH secretion is inhibited. A continuous undersecretion of thyroxin gives a lower metabolic rate, which causes decreased usage of nutrients, so excess nutrients are stored as fat and body mass increases.

Blood glucose

Blood glucose too high	Blood glucose too low
Detected by the islets of Langerhans in the pancreas	Detected by the islets of Langerhans in the pancreas
Insulin is secreted	Glucagon is secreted
Stimulates absorption of glucose from the blood into the cells; stimulates the liver and muscles to convert glucose to glycogen; increases cellular respiration which uses up glucose	Stimulates the conversion of glycogen to glucose in the liver, which is released into the blood
Blood glucose decreases to normal	Blood glucose increases to normal

Diabetes mellitus. In type 1 the immune system destroys the insulin producing cells, so no insulin is produced, blood glucose stays high and the person must inject insulin daily. In type 2 some insulin is produced but the target cells (liver and muscle cells) respond less to it. Excess glucose can be tested for in blood or urine.

Thermoregulation

Hot day	Cold day
Arterioles in the skin dilate (vasodilation)	Arterioles constrict (vasoconstriction)
MORE blood flows to the surface of the skin	LESS blood flows to the surface of the skin
MORE heat is lost by radiation and convection	Heat is retained, less heat is lost
Sweat glands become more active, more sweat is produced and transported to the skin surface, evaporation cools the body	Sweat glands are less active, less sweat is produced

Salt balance

Receptor cells detect the low salt level, the adrenal glands are stimulated, more aldosterone is secreted, in the renal tubules the reabsorption of salt is increased into the surrounding blood capillaries, so less salt is excreted.

Adrenalin in an emergency

It stimulates the breathing muscles, which increases the rate and depth of breathing so more oxygen is inhaled. It stimulates the heart muscle, causing an increase in heart rate and blood pressure, so oxygen and glucose are transported faster to the muscles.

Plant responses to the environment

The report is blunt about this topic: "It is a small section and constituted 13 marks in the question paper. This is almost a guarantee that it will feature in every examination, yet it is overlooked by teachers." There are only three hormones and three growth responses to know.

Hormone	Effects
Auxins	Stimulate cell elongation, cause phototropism and geotropism, promote apical dominance (inhibit lateral branches), promote fruit development. Used in herbicides.
Gibberellins	Stimulate seed germination, stimulate stem elongation, stimulate flowering and fruit development.
Abscisic acid	Promotes dormancy of seeds and buds, promotes ageing and abscission of leaves and fruit, stimulates closing of stomata during water stress.

Phototropism, the answer that scores

The seedling is exposed to unilateral light. Auxins diffuse to the dark side of the shoot. The higher concentration of auxins on the dark side stimulates more cell elongation on that side. There is less growth on the lit side, so the shoot bends towards the light.

Geotropism

In a horizontal shoot auxins accumulate on the lower side, causing more elongation there, so the shoot bends upwards (negatively geotropic). In a root, the same high auxin concentration on the lower side inhibits elongation, so the root bends downwards (positively geotropic).

Scientific investigations and exam skills

The two investigation questions in 2025 scored 33% and 40%, the worst in the paper. This section is worth more to you than any content revision.

Variables

• Independent variable: what the investigator changes, the cause. State what it is, not a step in the method. "Age", not "two-year-old boys".
• Dependent variable: what is measured, the effect. "Height", not "average height".
• Controlled (fixed) variables: everything kept the same. Start these answers with the word "same".

Validity versus reliability

Validity	Reliability
About fairness. All variables controlled except the one being tested.	About repeatability. Would you get the same result again?
To improve it, name factors kept constant, starting with "same".	To improve it, increase the sample size, repeat the investigation, take many measurements.
Answer must be specific to the extract given.	Answer must quote the actual numbers or duration in the extract.

Never mention both validity and reliability in one answer. The 2025 report records this as a direct cause of lost marks, because it shows you cannot tell them apart.

Hypothesis

Two variables, a stated relationship between them, testable, independent variable first (cause) then dependent variable (effect).

Conclusion

The conclusion must link to the aim, be deduced from the results, and contain the same two variables that appear in the aim. In 2025 candidates wrote "growth hormone" when the memo required "added growth hormone".

Planning steps

Start each planning step with the word "Decide". Decide on the sample size, decide on the venue, decide which measuring technique to use, decide how to record results.

Graphs

• Use a ruler. Freehand bars lose the mark for equal width and spacing.
• Do not transpose the axes. Independent variable on the X axis.
• Label day 0 or the starting value on the X axis, and use the specific values given, not ranges.
• Put units on the axis labels, not only in the final answer.
• The caption must include both variables, speak to the data shown, and identify the country, year or group.

Calculations

Show every step. Include the unit in each step, not only in the final answer. Bring a calculator and a ruler. Percentage increase is (new minus old) divided by old, times 100.

Reading the marks and the instructional verbs

Verb	What the marker expects
Name, State	The word only, no discussion
Identify	Name the essential characteristic
List	Items only, no detail
Describe	How something happens, the main points in order
Explain	How AND why, in cause and effect or statement and reason
Compare	Similarities and differences
Tabulate	Draw a table, items must correspond row by row, one mark is for the table itself
Calculate	Numerical answer with all working and units
Discuss	Consider all the information and reach a conclusion

Underline the instructional verb as you read. Then check the mark allocation: 3 marks almost never means one sentence, and a question worth 2 marks that says "give TWO" needs two separate points.

If a question asks for the LETTER and the NAME, giving only one of them scores nothing. If it says "name AND describe", naming alone scores nothing for the naming mark.

Exam-style questions with memos

Show memo: Explain TWO ways in which the lens is structurally suited to its function. (4)

The lens is transparent, to allow light to pass through. The lens is biconvex, for the refraction of light. The lens is elastic and can change shape or convexity. Any two, each worth two marks.

Show memo: Describe the process of hearing from the time sound waves reach the tympanic membrane. (6)

The tympanic membrane vibrates and transmits the vibrations to the ossicles in the middle ear. The ossicles amplify the vibrations to the oval window. Pressure waves form in the cochlea. Receptors in the organ of Corti are stimulated. Impulses are transmitted via the auditory nerve to the cerebrum to be interpreted.

Show memo: Describe the role of the ear in maintaining balance. (6)

Cristae are stimulated by a change in the speed or direction of movement of the head. Maculae are stimulated by a change in the position of the head. This generates an impulse, which is transmitted by the auditory nerve to the cerebellum for interpretation. The cerebellum sends an impulse to the skeletal muscles to restore balance.

Show memo: Explain how a concussion affecting the cerebrum does not affect heart rate. (2)

The medulla oblongata controls heart rate, and it is not affected by the concussion.

Show memo: Describe how the muscles in the iris enable a person to see in dim light. (4)

Radial muscles contract and circular muscles relax. The pupil widens or dilates. More light enters the eye.

Show memo: Describe TWO ways in which insulin decreases blood glucose levels. (4)

It stimulates the absorption of glucose from the blood into the cells. It stimulates the liver or muscles to convert glucose to glycogen. It causes increased cellular respiration which utilises glucose. Any two, each worth two marks.

Show memo: Describe the role of the pituitary gland in correcting a low thyroxin level. (4)

The thyroxin level is low. The pituitary gland is stimulated. More TSH is secreted, which stimulates the thyroid gland to secrete more thyroxin.

Show memo: Explain how auxins cause a seedling to bend towards unilateral light. (5)

The seedlings bend towards the light because they were exposed to light from one side. Auxins diffuse to the dark side of the seedling. The high concentration of auxins on the dark side stimulates cell elongation on that side. There is less growth on the lit side, so the stem bends towards the light.

Further reading and where to go next

• 2025 NSC Diagnostic Report, Chapter 8. Sections 8.2 to 8.4 are Paper 1. Read the "Common errors and misconceptions" under each question, they are the source of the confusable pairs table above.
• 2024 NSC Diagnostic Report, Chapter 8. The 2025 report repeatedly refers back to it, particularly for meiosis teaching tips and blood group notation.
• CAPS Examination Guidelines. The report advises learning the process descriptions given there rather than longer textbook versions, because going beyond the prescripts confuses learners.
• Past DBE papers, used as daily activities rather than as mock exams. But do not pre-empt: the report warns that candidates who see the word "thermoregulation" launch into a memorised answer from a previous paper instead of reading the new context.

One-page summary

• Paper 1 is 150 marks. Reproductive strategies (8 marks) and plant responses (13 marks) are compulsory and are the easiest marks in the paper.
• The weakest 2025 items were both scientific investigations, thermoregulation, hearing and balance, and accommodation. All application, not content.
• Quantify every physiological answer: MORE blood flows, LESS water is excreted, HIGHER progesterone.
• Accommodation is about distance and ciliary muscles. The pupillary mechanism is about light intensity and circular and radial muscles. Never mix them.
• Cristae detect speed and direction. Maculae detect position. Both send impulses along the auditory nerve to the cerebellum.
• Insulin converts glucose to glycogen. Glucagon converts glycogen to glucose. Glucagon is the hormone, glycogen is the store.
• Chorion is the membrane, choroid is in the eye. Oogenesis is the process, ovulation is the event.
• Validity is fairness and "same". Reliability is repeats and sample size. Never both in one answer.
• A variable is what is measured: height, age. Not "average height" or "two-year-old boys".
• Describe means how. Explain means how and why. Underline the verb before you write.
• Give the full name: central nervous system, not central. Give the letter AND the name when both are asked.
• Bring a calculator and a ruler.