science test

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define homeostasis + why is it important (2.1)

Homeostasis is the self regulating process where an organism maintains a stable internal environment despite external changes. It is important because cells need very specific conditions to function properly, which is why homeostasis must be maintained.

sensory receptors + where are they found? (2.1)

photoreceptor // detects light // found in eye (retina)

chemoreceptors // detects chemicals // found in nose, tongue and other parts of the body

mechanoreceptors // detects pressure touch and vibration // found in skin, ears, muscles and joints

thermoreceptors // detects temperature // found in skin and body

nociceptors // detects potential tissue damage // found throughout the body

describe examples of responses to stimuli (2.1)

A response to a stimulus is how a living organism reacts to a change inside/outside its body to stay alive and balanced. A stimulus is the signal or change in the environment, and the response is the action taken. (sunflower - turns its head to follow the sun across the sky so it can capture more light for energy.)

stimulus response model (2.1)

• stimulus (change in the environment, e.g., touching a hot pan)

• receptor (body part that detects the change, e.g., heat sensors in your skin)

• control center (the brain or spinal cord that processes the signal and decides what to do)

• effector (the muscle or gland that receives the order, e.g., arm muscles)

• response (the final action taken, e.g., pulling your hand away quickly)

how does the stimulus response model create a response (2.2)

First, the stimulus triggers the receptor, which sends an electrical signal along sensory nerves. Next, the control center evaluates this signal and instantly determines the necessary safety or balancing action. Finally, it sends a command to the effector, which physically executes the movement or release of chemicals to create the final response.

explain the role of feedback loops in maintaining homeostasis using body temperature and blood glucose levels as examples. (2.2)

When a human is exposed to a lower external temperature than normal, this is detected by special receptor cells. These receptors transmit information about the reduced temperature to the control centre in the brain, which triggers effector cells in the muscles. The effectors cause us to get goosebumps and to shiver and trigger vasoconstriction (narrowing of blood vessels). This helps to prevent heat loss.

Blood sugar levels are controlled by the hormones insulin and glucagon. When blood sugar levels become higher (e.g. after a meal), insulin sends a signal to the liver, muscles and other cells to take up the excess glucose (sugar) to be stored as body fat or as glycogen in the liver and muscles.

When blood sugar levels are too low, the hormone glucagon signals the liver to break down glycogen into glucose, which enters the bloodstream and raises the levels back to normal.

identify and describe the role of specialised neurons (2.3)

soma - is a large cell body containing the nucleus and organelles where essential metabolic processes occur to maintain cell survival

dendrites - they branch out from this cell body, they are fibres that convert chemical information from other neurons or receptor cells into electrical signals and is where incoming information enters.

axon - is long and thin (or nerve fibre), where nerve impulses are carried along to other neurons or effectors.

myelin sheath - a protective fatty layer that covers and insulates the axon, it improves the conduction speed of electrical impulses along the axon, but require additional space and energy

axon terminal - is at the end of the nerve, the gap between this and the next neuron is known as the synapse

how does info travel through neurons (2.3)

A message travels along one neuron, and then chemicals called neurotransmitters are released from the axon terminal (they are chemical messengers that carries a chemical message from one neuron to another).

These cross the gap between neurons- the synapse- and enter the dendrites of the next neuron, starting up a new nerve impulse.

Movement of an impulse along a neuron is always one way:

Dendrites → cell body → axon →synapse

what are the divisions of the nervous system

The nervous system is divided into two primary parts, which are the central nervous system and the peripheral nervous system.

The central nervous system consists of the brain and spinal cord, serving as the main control center that processes information and coordinates bodily responses.

The peripheral nervous system consists of all the nerves that branch out from the central nervous system to connect it to the rest of the body.

This peripheral system is further split into a sensory division that brings information into the brain and spinal cord, and a motor division that sends signals out to muscles and glands.

Within the motor division, the somatic nervous system controls voluntary movements of skeletal muscles, while the autonomic nervous system manages involuntary functions like heart rate and digestion.

Finally, the autonomic system is subdivided into the sympathetic system for stress and fight-or-flight responses, the parasympathetic system for resting and digesting, and the enteric system which independently regulates the gastrointestinal tract.

3 types of neurons (2.3)

sensory - (afferent) neurons. These collect information from the environment and transmit information TO the central nervous system for processing.

motor - (efferent) neurons. These communicate information FROM the central nervous system to tissues and organs throughout the body, which then allow for movement.

interneurons - these neurons make up the majority of neurons in the body and are essential for transmitting information between the sensory and motor neurons.

what is the importance of reflex arcs in responding to stimuli? (2.3)

Reflex arcs protect the body from harm by triggering instant, automatic responses before the brain even registers the danger.

describe the function and structure of the endocrine system? (2.4)

The endocrine system works alongside the nervous system to coordinate vital body processes through the release of hormones. These chemical messengers travel through the bloodstream to distinct target organs, where they manage long-term changes such as metabolic rate, physical growth, fluid balance, and reproductive cycles. The structural foundation of the endocrine system relies on ductless glands that are physically separated and scattered throughout the human body, from the brain down to the pelvis.

describe the process of sexual and asexual reproduction (1.1)

asexual: Asexual reproduction involves only a single parent and produces offspring that are exact genetic copies, or clones, of that parents. Methods include binary fission, fragmentation, budding and vegetative propagation.

sexual: Involves the fusion of two gametes (from two parents).

Gametes AKA germline cells (eggs and sperm) are produced in the gonads (ovaries and testes) via meiosis.

Gametes contain genetic material.

Gametes fuse together during fertilisation to produce a zygote which then develops into the animal or plant.

describe the process in which single celled organisms reproduce (1.1)

Single-celled organisms primarily reproduce asexually through a process where a single parent cell splits to create genetically identical offspring. First, the organism copies its genetic material (DNA) so each new cell receives a complete set of instructions. The cell then grows larger before dividing its cytoplasm and outer membrane down the middle.

state the differences of sexual and asexual reproduction (1.1)

Sexual reproduction requires two parents and involves the fusion of male and female gametes, leading to offspring that possess a unique blend of genetic material. This process generates high genetic diversity, which helps populations adapt to changing environments, though it requires more time and energy. In contrast, asexual reproduction involves just a single parent producing offspring without the fusion of gametes. The resulting offspring are genetically identical clones of the parent, allowing for rapid and highly energy-efficient population growth, though it leaves the species more vulnerable to sudden environmental changes or diseases due to the lack of genetic variation.

compare the advantages and disadvantages of each reproduction method (1.1)

sexual reproduction advantages + disadvantages:

• genetic diversity (A)

• environmental adaptation (A)

• high energy cost (D)

• slower population growth (D)

asexual reproduction advantages + disadvantages

• high speed + efficiency (A)

• successful trait preservation (A)

• zero genetic variation (D)

• high risk of extinction (D)

identify and describe what structures are needed for human reproduction (1.2)

In males, the testes produce sperm cells and the hormone testosterone, while external structures like the penis help deliver semen into the female reproductive tract. In females, the ovaries produce egg cells and hormones like estrogen, which regulate the reproductive cycle. When a sperm cell fertilizes an egg in the fallopian tubes, the resulting embryo moves to the uterus, a muscular organ that protects and nourishes the developing baby until birth.

explain the role of internal and external fertilisation in animal reproduction (1.3)

External fertilisation occurs in aquatic environments where animals release large quantities of gametes into the water, relying on the fluid medium for the sperm to swim and reach the eggs. This method requires minimal physical contact between parents but leaves the offspring vulnerable to predators and currents. In contrast, internal fertilisation takes place inside the female reproductive tract, which shields the gametes from drying out and protects the developing embryo from harsh land environments

provide examples of organisms that use each type of fertilisation (1.3)

external fertilisation:

• frogs

• salmon

• sea urchins

• coral

internal fertilisation:

• humans

• penguins

• kangaroos

• crocodiles

describe the methods of reproduction in different plants (1.4)

Flowering plants rely on sexual reproduction, where pollinators transfer pollen from the anther to the stigma of another flower. The pollen travels down the style to fertilise the egg inside the ovary, forming a seed that grows into a genetically unique plant. To germinate, these seeds disperse using wind, water, gravity, animals, or fire. Conversely, asexual reproduction produces identical plants without fertilisation. This occurs through budding (a bud of cells grows, falls off, and becomes a new plant , native parsnip) releasing spores (reproductive cells released without needing fertilisation , ferns), or vegetative propagation (methods like runners rooting in soil, branching roots sprouting new growth, thickened tubers) and fragmentation where broken pieces grow into independent plants.