Biology.

Question 1

Diffusion

Answer 1

-Movement of molecules from a high concentration to a low concentration. Move in random movement.
- Across a partially permeable membrane
Helps living organisms:
* Obtain requirements
* Get rid of waste prodcuts
* carry out gas exchange (for respiration)
- Uses knentic enegy

Examples
- Plants require oxygen for respiration all the time
- carbon dioxide for photosynthesis

Question 2

Water

Answer 2

• Substances that dissolve in water can move around the body/plant easily
• Nutrients in the body dissolve in water to be carried all around
• Waste materials like urea and excess salts can dissolve in water and be flushed out of the body in urine.
• Is important in the cytoplasm, helping chemical reactions take place to keep the cell alive

Question 3

Osmosis

Answer 3

• Water moves in/out of cell
• Osmosis is the diffusion of water molecules from a dilute solution (more water, less solute) to a more concentrated solution (less water, more solute ) across a partially permeable membrane
• Water moves down the concentration gradient
• Partially permeable means it allows small molecules (water) go through but not larger molecules (solute molecules)

Question 4

Osmosis: Plants

Answer 4

• when water enters the plant cell vacuole gets bigger (expands)
• when it expands it pushes the cell membrane against the cell wall
• the water makes the plant rigid and turgid
• good for support, strength
• The cell wall prevents too much water from entering
• If a plant doesn’t get enough water (wilts)
• When plant cells are placed in a solution that has a higher water potential (dilute solution) than inside the cells then water moves into the plant cells (makes Turgid)
• When plant cells are placed in a concentrated solution lower water potential) than inside the cells water molecules will move out of the plant cells (flaccid)

Question 5

Active Trasport

Answer 5

• The movement of particles through a cell membrane from a lower concentration to a higher concentration using energy from respiration
• Vital process of movement of molecules/ions
• uptake of glucose in the villi of the small intestine and by kidney tubules
• Uptake of ions from soil water by root hair cells

Question 6

Protein Carriers

Answer 6

• Active transport works by using protein carriers to move specific molecules from a low concentration to a high concentration
  Steps
  1.) Substance combines with carrier protein molecule in the cell membrane
  2.) Energy from respiration powers the protein to change shape and transport the substance into or out of the cell.
  3.) Substance is realsed into the cell

Question 7

Mammalian Nervous System

Answer 7

Human nervous system consists:
-Central nervous system(CNS)
* Brain/spinal cord
-peripheral nervous system (PNS)
* All the nerves in the body
- allows us
* make sense of surroundings and respond
* Coordinate body functions
- Information is sent through the nervous system as nerve impulses (Nerve)

Question 8

Types of Neurones

Answer 8

Three main types of neurone:
* Sensory (Long): Carry impulses from sense organs to the CNS (brain/spinal cord).
* Relay (short): Found within the brain/spinal cord, connects sensory and motor neurons
* Motor (Long): Carry impulses from the brain/spinal cord to effectors (muscles or glands)

• Neurons have axons
• Axon: A long fibre that carries the impulse quickly and avoids delay
• Fatty sheath: Insulates the axon and has gaps called nodes, impulses jump between nodes, speeding up communication
• Dendrites: The cell body that receives impulses from other neurons, allowing connection to other neurons for efficient communication.

Question 9

The Reflex Arc

Answer 9

• Voluntary Responses
• When you make a conscious decision to carry out an action, it starts with your brain
  *Involuntary Response(reflex)
• Does not involve the brain of the reaction and is not aware until after the action is done. - - An automatic and quick response
• This helps minimize damage to the body

A reflex:
1.) A stimulus is detected by receptors in the body.
2.) A sensory neurone carries the electrical impulse to the spinal cord
3.) A relay neurone in the spinal cord passes the impulse to a motor neurone
4.) The motor neurone carries the impulse to an effector (muscle or gland)
5.) The effector produces a response, quick and automatic.

The Reflex pathway:
1.) stimulus
2.) receptor
3.) sensory neurone
4.) relay neurone
5.) motor neurone
6.) effector
7.) response

Question 10

Synapse

Answer 10

• Where two neurons meet/join,
• allow neurones to connect, forming a network throughout the nervous system
• Make sure impulses only go one way (from presynaptic to postsynaptic neurone)
  -Prevents confusion in the nervous system
• The electrical impulse travels along the first axon

1.) An electrical impulse reaches the end of the presynaptic neurone.
2.) The impulse causes vesicles to release neurotransmitters
3.) The neurotransmitter diffuses across the synaptic gap
4.) The neurotransmitter binds to specific receptors on the membrane of the postsynaptic neurone.
5.) triggers ion channels to open in the postsynaptic neurone, allowing the ions to enter. If enough ions enter, it generates a new electrical impulses
6.) The neurotransmitter is broken down by enzymes or reabsorbed to stop continuous stimulation.

Question 11

Sense organs/ Receptors

Answer 11

• Receptors are sets of special cells that sense changes in the environment. When they detect something, they trigger electrical signals in the body.
• Sense organs have receptors that react to specific changes like light, sound, or temperature.

Question 12

Eye structure

Answer 12

• The eye is a sense organ containing receptor cells that are sensitive to light

Cornea:
* A see-through front layer that refracts (bends) the light
Iris:
* The muscle that controls how much light enters through the pupil
Lens:
* see-through disc that changes shape to focus light onto the Retina
Retina:
* A layer of light receptor cells that detect light intensity and colour
Optic nerve:
* Sensory neurone that carries electrical impulses to the brain

Question 13

Pupil Reflex

Answer 13

• It is a reflex action that controls how much light enters the eye
• In dim light, the pupil dilates (gets bigger) to let in more light.
• In bright light, the pupil constricts (gets smaller) to let in less light and protect the retina from damage.

Question 14

Iris muscles

Answer 14

• The iris controls the size of the pupil
• contains two types of muscles:
• Circular muscles: form circles around the pupil
• Radial muscles:: start at the pupil and stretch outward toward the edge of the iris.
• Dim light
• Light receptors detect low light levels
• The radial muscles contract, pulling the pupil wider
• The circular muscles relax.
• As a result, the pupil dilates (gets bigger) to let in more light

-Bright light
* Light receptors detect high light levels
* The circular muscles contract, making the pupil smaller
* The radial muscles relax
* causes the pupil to constrict (get smaller), reducing light entry ( protecting the retina.)

Question 15

Eye accommodation:

Answer 15

• How the eye changes the shape of the lens to focus on near or distant objects.
• Ciliary muscles (ring-shaped muscles)
• Suspensory ligaments (thin fibres attached to the lens)

Eye accommodation near objects
* Ciliary muscles contract.
* Suspensory ligaments loosen
* The lens becomes more rounded (thicker)
* increases the refraction of light, helping focus on the close object

Eye accommodation for close objects
* Ciliary muscles relax
* Suspensory ligaments tighten
* The lens becomes thinner (flatter).
* decreases the refraction of light, allowing the lens to focus the light on the retina for clear vision of far objects.

Question 16

Rods/cones

Answer 16

• Rods/cones are receptor cells in the retina of the eye that detect light stimuli

Rods:
- Detect light at low levels, making them crucial for night vision
- Found all over the retina (except the blind spot)

Cones:
- three types of cones that detect light at three different wavelengths (red, green, and blue), enabling colour vision
- Cones are concentrated in the fovea, the part of the retina where light is focused through
- The fovea allows the brain to form sharp, coloured images.

Question 17

Hormones in Humans

Answer 17

Hormome:
- a chemical substance produced by a gland and carried through the bloodstream.
- Alter the activity of particular organs to cause a response or change.
- serve as messengers that transmit information within the body and triggers responses in different parts
- The glands that produce hormones in animals are part of the endocrine system.

Transport around the body:
- Endocrine glands have a rich blood supply to ensure hormones are quickly released into the blood plasma for fast travel
- hormones only affect cells that have specific target receptors which hormones bind to (cell membrane) (inside cell)

Liver
- The liver helps control/ maintain the balance of hormones in the bloodstream
- transforms or breaks down hormones that are in excess (ensures balance)

Question 18

Important hormones in the human body:

Answer 18

Hormone: Adrenaline
- Source: adrenal gland
- Role: Prepares body for “fight or “fight response
- Effect: Increases heart rate/breathing rate, Dilates pupil

Hormone: insulin
- Source: Pancreas
- Role: Lowers blood glucose levels
- Effect: Causes excess glucose in the blood to be taken up by muscles/Liver, converted into Glycogen (for storage)

Hormone: Testosterone
- Source: Testis
- Role: Sex hormone in males
- Effect: Hair,Voice deeper, Increase muscle mass/strength, growth of penis/testes

Hormone: Oestrogen
- Source: Ovaries
- Role: Sex hormone of the female
- Effect: Growth of breasts, widening of hips, lining of uterus to thicken after period, another hormone, progesterone, to control when the lining is built up, menstrual cycle begins

Question 19

Nervous/ Endocrine system

Answer 19

Nervous system:
- Made up of: neurones, brain, spinal cord
- Type of message: electrical impulse
- Speed of transmission: Very fast
- Length of effect: Short

Endocrine System:
- Made up of: Glands
- Type of message: Chemical hormone
- Speed of transmission: slower
- Length: Longer

Question 20

Glucagon

Answer 20

• Blood glucose levels are controlled by a negative feedback mechanism using two hormones: Insulin and Glucagon
• Both hormones are produced by the pancreas.
• When blood glucose levels fall, the pancreas releases glucagon

Glucagon:
- Stimulates the liver and muscle cells.
- Causes them to convert stored glycogen back into glucose.
- This glucose is released into the blood, raising blood sugar levels to normal.

Question 21

Hormone adrenaline

Answer 21

• Adrenaline is a hormone produced in situations where the body may be in danger
• Increasing blood glucose concentration for increased respiration in muscle cells
• Increasing pulse rate and breathing rate so glucose and oxygen can be delivered to muscle cells
• Dilating pupils to allow as much light as possible to reach the retina so more information can be sent to the brain

Question 22

Homeostasis

Answer 22

• keeping the inside of your body stable/balanced, even when the outside environment changes
• The body must keep conditions like temperature, water levels, and blood glucose within the limits so cells can function properly.
• if blood glucose gets too high and isn’t solved, it can harm the body and eventually lead to death

Question 23

Role of Insulin

Answer 23

• After a meal, blood glucose levels rise
• Insulin is released by the pancreas into the blood
• Insulin helps lower blood glucose by:
• tells the liver and muscles to convert extra glucose into glycogen for storage.
• This stops glucose from being lost in urine
• Later, if glucose levels drop, glycogen is turned back into glucose for usage

Question 24

Negative Feedback

Answer 24

• helps the body keep internal conditions stable (e.g., temperature, blood glucose, water levels)
• responds when something moves away from the normal level, and brings it back.

How It Works:
- If an internal condition in the body rises too high, the body acts to reduce it.
- If an internal condition in the body falls too low, the body acts to increase it.
- This cycle repeats constantly to keep conditions in a safe range

Question 25

Type 1 Diabetes

Answer 25

- occurs when the insulin-producing cells in the pancreas stop working - As a result, blood glucose levels become too high. Treatment: - Need to inject insulin to lower blood glucose levels Helps the liver convert excess glucose into glycogen (lowering glucose levels) Symptoms: * Extreme thirst * Weakness/tiredness * blurred vision * Weight loss Managing Type 1 Diabetes: - People need to monitor their blood glucose regularly - Adjust insulin levels based on their diet and physical activity: * Diet: Eat foods that won’t cause large spikes in glucose. * Exercise: Increases respiration in muscles, which helps lower blood glucose levels.

Question 26

The Skin/Homeostasis

Answer 26

- For optimal function, the human body needs to maintain a temperature of around 37°C (this is when enzymes work best). - If body temperature increases above this temperature, enzymes will denature and become less effective - if body temperature drops below this temperature, enzymes will work more slowly and become less effective. How Temperature is Controlled: - The brain monitors blood temperature and has special receptors to detect changes. - The skin also has temperature receptors (thermoreceptors) that send nerve signals to the brain ( Via Sensory neurones) - When the brain receives this info, it sends signals to the skin to help adjust body temperature How the Skin Helps Control Temperature: - Fatty tissue under the skin helps insulate the body, stopping too much heat from escaping. - If the body gets too hot/cold, the brain adjusts skin responses to maintain the right temperature for enzyme function.

Question 27

Responses to changes in temperature:

Answer 27

When we are hot: - sweat is secreted by seat glands - This cools the skin by evaporation - Heat energy from the body is lost as liquid water in sweat becomes water vapour - Hair falls flat, allowing air to freely circulate, which increases heat transfer to the environment by radiation When we are cold: - Skeletal muscles contract, and we shiver - The involuntary muscle contractions need energy from respiration, and some of this is released as heat - small muscles at the base of hair follicles contract, causing hairs to stand up - This traps a layer of air close to the skin, - The trapped air acts as an insulator - reduces heat loss by radiation, helping the body retain warmth.

Question 28

Vasoconstriction/ Vasodilation

Answer 28

Vasoconstriction (When cold) - Blood flow in capillaries slows down because arterioles get narrower This reduces the amount of heat lost from blood by radiation as less blood flows through the surface of the skin Vasodilation (When hot) - Blood flow in capillaries increase because arterioles get wider - More heat is lost from the blood by radiation - Helps the body cool down

Question 29

Pathogens

Answer 29

- A pathogen is a microorganism that causes disease - Diseases caused by pathogens are called transmissible diseases because they can spread from one person to another Ways Pathogens Spread: * Direct contact – through body fluids (like blood or semen) * Indirect contact – through air, contaminated surfaces, food, water, vectors (like mosquitoes) The body protects itself in 3 main ways from diseases: 1.) Mechanical Barriers - Physical structures that block pathogens * Skin: Covers the body and blocks entry; forms a scab if cut to seal the wound * Nose hairs: Trap pathogens, stopping them from reaching the lungs 2.) Chemical Barriers - (Chemicals that destroy/trap pathogens) * Mucus: Sticky fluid that traps pathogens; removed by coughing, sneezing, swallowing * Stomach acid: Hydrochloric acid in the stomach kills pathogens 3.) White Blood Cells - (Fight off pathogens once inside the body) * Phagocytosis: Some white blood cells engulf and digest pathogens. * Antibodies: - Stick pathogens together - Destroy them Stop them from moving or infecting cells

Question 30

Controlling the Spread of Disease

Answer 30

* Clean water supply: - Prevents diseases like cholera by ensuring drinking water is free from pathogen * Hygienic food prep: - Washing hands, cooking food properly prevents food contamination * Personal hygiene: - Using tissues and washing hands reduces the spread of by the air, diseases like colds/flu. * Waste disposal - Properly getting rid of waste lowers the number of pests that spread diseases * Sewage treatment - Removes harmful pathogens from human waste before it enters the environment

Question 31

Active Immunity

Answer 31

- Active immunity is when the body makes its own antibodies and develops memory cells for future protection against pathogens How Active Immunity Happens: * Natural infection - The body gets infected by a pathogen - Lymphocytes make specific antibodies to fight pathogens - Memory cells are made for future protection * Vaccination: - Introduces a harmless version of the pathogen - The body still makes antibodies and memory cells, without getting sick. -Active immunity is slow acting ((takes time to develop after first exposure - Provides long-lasting immunity protection (due to memory cells that stay in the body)

Question 32

Antigen

Answer 32

Antigen: - Antigens are protein molecules on the surface of all cells - Lymphocytes (a type of white blood cell) can recognize antigens that do not belong in the body - In response, lymphocytes produce antibodies, proteins that match the shape of the antigen - They help the immune system destroy it Antibodies - are special proteins made by lymphocytes (a type of white blood cell) in response to foreign antigens - They stick to the antigens on pathogens - causes agglutination (clumping), which makes it harder for pathogens to move or spread. - The clumps attract phagocytes (another type of white blood cell), which come and engulf (eat) and destroy the pathogens.

Question 33

Immunity

Answer 33

How immunity works: - When a lymphocyte (a type of white blood cell) first meets a new pathogen, it takes a few days to produce the correct antibodies, the person feels sick. - After this first encounter, memory cells are made. These cells ("remember") how to make the right antibodies - If the same pathogen enters the body again, these memory cells help the body respond much faster, producing more antibodies quickly (the person doesn’t get sick again) - However, not all pathogens stay the same, some mutate and change their antigens, so the memory cells from before can’t recognize them. That’s why you can catch some diseases (E.g, the flu) more than once.

Question 34

Vaccination

Answer 34

- Vaccines protect against specific diseases without needing to be infected by the live, dangerous pathogen - The more people vaccinated in a population, the greater the overall level of protection How Vaccines Work: - A dead/ altered form of the pathogen is introduced into the body * This pathogen contains the same antigens as the live one, but cannot cause a disease - The body’s lymphocytes recognize the antigens and make antibodies that match their shape - These antibodies attach to the antigens, helping to destroy the pathogen - Memory cells are also made and stay in the blood Why It Works Long-Term: - If the real pathogen later infects the body, memory cells respond faster, producing antibodies much faster and in larger amounts - prevents illness, giving long-lasting immunity

Question 35

Preventing the Spread of Disease

Answer 35

* Herd Immunity - When a large enough percentage of a population is vaccinated, it becomes hard for the pathogen to spread - This is because there are very few unvaccinated people for the pathogen to infect and reproduce in Low Vaccination Rates: - If vaccination levels drop, it increases the risk of mass infection. - Unvaccinated individuals are more likely to: * catch the disease * Spread it to others Importance of Herd Immunity: - prevents epidemics and pandemics.

Question 36

Passive immunity/ Breatfeeding

Answer 36

- Passive immunity is when antibodies are received from another individual, not produced by the body itself - gives quick but short-term protection against pathogens. -In breastfeeding, a mother’s antibodies pass to the baby through breast milk - helps protect the baby from infections - Since the baby’s body doesn’t make its own antibodies or memory cells, the protection doesn’t last long

Question 37

Cholera

Answer 37

What Cholera Does: - Cholera bacteria are ingested through contaminated food or water -(Vibrio cholerae bacteria), cause the disease cholera - In the small intestine, they: * Attach to the intestinal wall *.Release a toxin Effect of the Toxin: - The toxin causes cells lining the intestine to release chloride ions into the intestine’s lumen - This lowers the water potential in the lumen - As a result, water moves out of the cells by osmosis into the intestine Outcome: - This leads to loss of water and ions from the body in the form of watery diarrhoea - Dehydration can follow, and without treatment, may lead to organ failure/death Treatment: - Oral rehydration therapy (ORT) * a mixture of water, salt, and sugar that helps replace lost fluids and ions

Question 38

Asexual Reproduction

Answer 38

- A process that involves only one parent, with no fusion of gametes and no mixing of genetic material Examples of Asexual Reproduction: - Bacteria * Reproduce by binary fission, making exact genetic copies - Plants * Bulbs and tubers (e.g. onions, potatoes): underground food storage organs that sprout new plants. * (E.g. Strawberry) plants reproduce asexually by growing side shoots called runners, which grow small baby plants called plantlets. These plantlets grow roots and eventually break off to live on their own as new, identical plants. Advantages of Asexual Reproduction: - Wild species: * Rapid population growth * Energy and time-efficient * Faster than sexual reproduction - Crop plants * can be grown to have useful features like high yield, disease resistance, or drought resistance * made to have similar size, shape, and quality, which is important for selling them in shops. * Production of crops can be faster Disadvantages of Asexual Reproduction: - Wild species * No genetic variation * Vulnerable to environmental changes * Slow evolution - Crop plants * No adaptation to climate change * Human input needed * Disease in the parent spreads to the offspring

Question 39

Sexual reproduction

Answer 39

- A process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other - Fertilisation: As the fusion of gamete nuclei Gametes - Is a sex cell - In animals * sperm (male) and ovum (female) - In plants * pollen nucleus (male) and ovum (female) - In human beings, a normal body cell contains 46 chromosomes, but each gamete contains 23 chromosomes - Gametes have a haploid nucleus, meaning 23 chromosomes in humans (half the normal amount) - because they only contain one copy of each chromosome Zygote - A Fertilised Egg Cell - When the male and female gametes fuse, they become a zygote - Has a diploid nucleus, meaning 46 chromosomes in humans (23 pairs) Advantages of sexual reproduction - Wild species * Increase genetic variation * The species can adapt to new environments (increase level of survival) * Diseases are less likely - Crop plants * genetic variation * cope better with weather changes Disadvantages of sexual reproduction - Wild species * takes time/energy * Difficult for isolated species to reproduce - Crop plants * Because of variation, some new plants might not grow as well as the parent plant: - Be weaker/ smaller - Produce fewer fruits/ seeds - Be less resistant to diseases

Question 40

Haploid/Diploid Cells

Answer 40

- Haploid cells have half the number of chromosomes found in normal body cells * These are the gametes (sperm and egg) * In humans, this means 23 chromosomes (not in pairs) - Diploid cells have the full number of chromosomes (arranged in pairs) * This includes body cells and the zygote (fertilised egg) * In humans, this means 46 chromosomes (23 pairs) Key points: * Gametes are haploid, so that when they combine during fertilisation, the resulting zygote is diploid * The zygote remains diploid as it divides and develops into an embryo and later a fetus

Question 41

Sexual Reproduction in Plants

Answer 41

- Flowers are reproductive organs enabling fertilisation - Male gametes = pollen (in anthers); Female gametes = ovules (in ovary) - Pollination = transfer of pollen from anther to stigma (via insects or wind). Insect-Pollinated Flowers: - adapted to allow insects to collect pollen from the male parts of the flower and easily transfer it to the female parts of another plant Sepal: Protects the bud (unopened flower ) Petals: Bright and colourful to attract insects Anther: Produces and releases pollen Filament: Provide support to anther Stigma: Sticky surface that catches pollen grains Style: A tube that connects the stigma and ovary Ovary: Contains the ovules Ovule: inside the ovary that contains the female gametes

Question 42

Wind pollinated flowers

Answer 42

- Wind-pollinated flowers are adapted so that wind can easily catch pollen grains and carry them to the stigmas of other flowers - Anthers and stigmas hang outside the flowers so tha: * Pollen can easily be blown away by the wind * Pollen can easily be caught by the stigmas of other flowers Pollination & fertilisation: - Insect-pollinated flowers produce larger/heavier pollen grains that often contain (spikes/hooks) on the outside so they are better able to stick to insects - Wind-pollinated flowers produce small, lightweight pollen grains that can be caught and carried easily by the wind Pollination: The transfer of pollen grains from an anther to a stigma Fertilisation in plants: The fusion of a pollen nucleus with an ovum nucleus * After pollination, the pollen nuclei travel to the ovule and fuse with female gametes in a process called fertilisation

Question 43

Factors Affecting Germination of Seeds

Answer 43

Germination: is the start of growth in the seed 3 factors for successful germination: - water * Helps seed swell and activate enzymes for growth -Oxygen * Required for energy release during germination - Warmth * Higher temperatures speed up germination by controlling enzyme activity. - Carbon dioxide (isn’t necessary) But doesn’t slow germination

Question 44

Self- & Cross-Pollination:

Answer 44

cross-pollination: occurs when the pollen from one plant is transferred to the stigma of another plant of the same species - most plants carry out pollination as it (improves genetic variation) Self-pollination: Pollen from the same plant fertilizes its own stigma, reducing genetic variation - all the gametes come from the same parent (and are therefore genetically identical) Disadvantages of self-pollination: - Less adaptability to changing environments Disadvantages of cross-pollination: - relies completely on the presence of pollinators, and this can be a problem if those pollinators are missing (no pollination)

Question 45

Sexual Reproduction in Humans

Answer 45

Males - Prostate gland: Produces fluid (called semen) that provides nutrients for sperm cells - Sperm duct: Transports sperm, mixes it with fluids from glands before passing it into the urethra for ejaculation - Urethra: Tube inside the penis that carries either urine or semen - Testis: Produces sperm (male gametes) and the hormone testosterone (located in the scrotum) - Scrotum: Sac that supports the testes outside the body, keeping sperm at a slightly cooler temperature than body heat - Penis: Transfers urine out of the body and allows semen to enter the vagina during (sexual intercourse) Females: - Oviduct: Connects the ovary to the uterus and has ciliated cells that move the ovum; (fertilisation happens here) - Ovary: Produces and releases ova (egg cells); they mature in response to hormones - Uterus: An organ with a soft lining where the fertilised egg implants and develops into a foetus. - Cervix: at the base of the uterus that holds the foetus in place during pregnancy - Vagina: where the penis enters during intercourse and sperm is placed

Question 46

Pollen tube formation

Answer 46

* After pollination, a pollen tube grows down the style to the ovary * Pollen nuclei travel down the tube * The nuclei enter the ovule and fuse with the nucleus of the female gamete (fertilisation) * After fertilisation, the ovules develop into seeds and the ovary develops into a fruit

Question 47

Gametes & Fertilisation (humans)

Answer 47

Fertilisation is the fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell) * It occurs in the oviducts Gametes have adaptations: * to increase the chances of fertilisation and successful development of an embryo - The gametes are highly specialised cells with adaptive features designed to maximise the chances of successful reproduction Adaptive features of the gametes: - Sprem * Has a flagellum (tail): Allows the sperm to swim towards the egg * Contains enzymes in the head (acrosome): To digest a path into the egg for fertilisation * Contains many mitochondria: To provide energy for movement of the flagellum - Egg * Cytoplasm contains a store of energy: To provide energy for the zygote (making more cells) to grow and develop after fertilisation. * Has a jelly-like coating that changes after fertilisation: Forms an impenetrable barrier to prevent other sperm from entering

Question 48

The placenta & umbilical cord:

Answer 48

- The placenta is an organ that develops during pregnancy to allow exchange of nutrients between the mother’s blood and the fetus’s blood - The umbilical cord connects the fetus to the placenta and carries blood to and from the fetus. How do nutrients/ waste move: - The fetus gets glucose, amino acids, fats, water, and oxygen from the mother’s blood to grow - Waste products like carbon dioxide and urea from the fetus are passed into the mother’s blood to be removed (by diffusion) How does diffusion happen efficiently: - All movement of substances is by diffusion (following concentration gradients) - The placenta is well adapted for diffusion: * Large surface area * Thin walls between blood vessels Protection against toxins and pathogens: - The placenta helps protect the fetus by blocking many toxins and pathogens. - Some small molecules (nicotine/ viruses can pass through

Question 48

Growth & Development of the Fetus

Answer 48

- After fertilisation in the oviduct, the zygote travels towards the uterus * This takes about 3 days, for the zygote to form a ball of cells known as an embryo - Implantation occurs in the uterus lining around day 6–7 - First 12 weeks: Organs start forming; nutrients pass from mother to embryo by diffusion. - After 12 weeks: (the fetus); organs are formed, and the placenta takes over as the nutrient exchange. - Remaining time (up to 9 months) is for growth in size - The fetus is surrounded by an amniotic sac filled with amniotic fluid, (which comes from the mother’s blood plasma) - This fluid cushions and protects the fetus by absorbing shocks from any bumps or movements to the mother’s abdomen during pregnancy

Question 49

Menstrual Cycle

Answer 49

- Starts in girls (around age 12) and is controlled by hormones - Lasts on average 28 days - Day 14: Ovulation egg released from ovary, and the egg then travels down the oviduct to the uterus - If the egg isn’t fertilised, the uterus lining breaks down and menstruation (a period) begins - Menstruation lasts 5–7 days, marking the start of the next cycle - After a period, the uterus lining thickens again to prepare for possible pregnancy

Question 50

Oestrogen and Progesterone

Answer 50

Oestrogen - Made by the follicle in the ovary - Stimulates growth of the uterine lining - slows FSH and LH after ovulation to prevent multiple eggs from maturing (in pituitary gland) - Oestrogen levels peak before ovulation Progesterone - Made by the corpus luteum after ovulation - maintains the thickened uterine lining - Slows FSH and LSH levels - If no fertilisation, progesterone levels fall, triggering menstruation - If pregnancy occurs, progesterone levels stay high to support the pregnancy

Question 51

Roles of FSH and LH

Answer 51

FSH: Follicle Stimulating Hormone - Made in the pituitary gland - Stimulates a follicle in the ovary to mature an egg - Stimulates egg maturation in the ovary - This triggers the release of oestrogen LH: Luteinising Hormone - Also from the pituitary gland. - Triggered by the rise of oestrogen - Causes ovulation (release of egg into oviduct) - Stimulates the formation of the corpus luteum, which makes progesterone. Stimulates the formation of the corpus luteum, which makes progesterone in the ovaries

Question 52

STIs & HIV/AIDS

Answer 52

- STIs (Sexually Transmitted Infections) - Spread through unprotected sex via the exchange of body fluids - An example of an STI is HIV (Human Immunodeficiency Virus) HIV can also spread through: * Infected blood transfusions * Mother to baby during pregnancy (through the placenta)/ breastfeeding

Question 53

How HIV Affects the Immune System

Answer 53

1.) Early Stage: After infection, the person may have mild flu-like symptoms 2.) Hidden Phase: The person may feel normal but is still infected and can pass on the virus 3.) Attack on Immune Cells: * HIV targets and enters lymphocytes (a type of white blood cell). * Lymphocytes make antibodies and destroy pathogens 4.) HIV’s Strategy * It changes its protein coat to avoid being recognised * make more copies of itself 5.) Immune System Breakdown * Over time, the number of lymphocytes drops. * Fewer antibodies are produced. * The body can’t fight off infections effectively 6.) AIDS (Acquired Immunodeficiency Syndrome) develops when the immune system is severely weakened

Question 54

Controlling the Spread of STIs

Answer 54

* Limiting the number of sexual partners an individual has * Not having unprotected sex (using condom) * getting tested if had unprotected sex * Raising awareness of STI

Question 55

Photosynthesis

Answer 55

Photosynthesis:the process by which plants manufacture carbohydrates from raw materials using energy from light - Green plants use carbon dioxide (from the air) and water (from the soil) to make glucose (a carbohydrate) - Oxygen is produced as a waste product and released - The process needs energy, which comes from sunlight absorbed by chlorophyll in the leaves Photosynthesis Equation: Carbon dioxide + water →→→→ Glucose + oxygen

Question 56

Chlorophyll

Answer 56

- a green pigment that is found in chloroplasts within plant cells * reflects green light, giving plants their green colour - Chlorophyll absorbs light energy, its role is to transfer energy from light into energy in chemicals, for the process of making carbohydrates, such as glucose - Photosynthesis will not occur in the absence of chlorophyll

Question 57

Use & Storage of Carbohydrates in Plants

Answer 57

- The carbohydrates produced by plants during photosynthesis can be used - Converted into starch molecules which act as an effective energy store -