Year 9 Science Semester Revision

Comprehensive question-and-answer revision flashcards covering Year 9 Science topics: Earth & Climate, Body Systems, Disease & Immunity, Reproduction, and Investigation Skills.

Which process removes carbon dioxide from the atmosphere, and which three processes return it?

Photosynthesis removes carbon dioxide from the atmosphere, while respiration, combustion, and decomposition return it.

What are the four spheres of the Earth and what does each comprise?

The atmosphere consists of the layer of gases surrounding Earth; the hydrosphere comprises all water (oceans, lakes, groundwater, ice, vapour); the geosphere includes solid rocks, soil, sediments, and the interior; and the biosphere includes all living things.

How does water move between Earth's spheres through the water cycle?

Water enters the atmosphere via evaporation from bodies of water/soil and transpiration from plant leaves, condenses into clouds, returns to the land and water via precipitation, and then moves through runoff, infiltration, or uptake by living organisms.

What role do decomposers play in the carbon cycle?

Decomposers such as bacteria and fungi break down dead organic matter and waste, releasing carbon dioxide into the atmosphere through cellular respiration and returning nutrients to the soil.

How do greenhouse gases warm the lower atmosphere?

Greenhouse gases absorb and re-emit outgoing infrared radiation, trapping heat in the lower atmosphere.

Which greenhouse gas is associated with livestock digestion, and which gas is released due to excess fertiliser use?

Methane ($CH_4$) is produced by cattle and sheep during digestion, and nitrous oxide ($N_2O$) is released when excess fertiliser is applied.

What are two major consequences of climate change on coral reefs?

Warmer waters cause coral bleaching (corals expel the algae supplying their energy), and increased dissolved $CO_2$ causes ocean acidification, hindering corals from building and maintaining calcium carbonate skeletons.

What are the differences between pre-combustion, post-combustion, and oxyfuel combustion capture?

Pre-combustion separates carbon from fuel-derived gas before combustion; post-combustion separates $CO_2$ from exhaust gases after burning; oxyfuel combustion burns fuel in pure oxygen rather than air to produce an exhaust that is easier to process for $CO_2$.

What structures compose the central nervous system (CNS) and peripheral nervous system (PNS)?

The CNS consists of the brain and spinal cord, whereas the PNS includes all nerves located outside the CNS.

What are the distinct functions of sensory neurons, interneurons, and motor neurons?

Sensory neurons carry impulses from receptors to the CNS, interneurons connect neurons within the CNS to process information, and motor neurons transmit impulses from the CNS to effectors (muscles or glands).

How is a nerve impulse transmitted across a synapse?

An electrical impulse reaching the presynaptic neuron triggers vesicles to release neurotransmitters into the synaptic cleft; these diffuse across the gap, bind to receptors on the postsynaptic neuron, and trigger a new impulse before being broken down or reabsorbed.

How do the somatic and autonomic nervous systems differ in function?

The somatic nervous system directs voluntary actions using skeletal muscles (e.g., walking, writing), while the autonomic nervous system regulates involuntary processes in organs and glands (e.g., heart rate, sweating, digestion).

How do nervous and endocrine communication compare in terms of message type, speed, and duration?

The nervous system uses electrical impulses and neurotransmitters for rapid, targeted, and short-lived responses; the endocrine system secretes hormones into the bloodstream for slower, wider-reaching, and longer-lasting responses.

What are the complementary functions of insulin and glucagon in maintaining blood glucose levels?

Insulin lowers elevated blood glucose by promoting cell uptake and storage as glycogen in liver and muscle cells; glucagon raises low blood glucose by prompting the liver to break down glycogen into glucose.

What are the primary roles of ghrelin, leptin, and dopamine?

Ghrelin is secreted by the stomach to increase hunger; leptin is released by fat tissue to signal satiety and reduce appetite; dopamine functions as a neurotransmitter linked to motivation, reinforcement, and reward.

What is homeostasis, and how does negative feedback contribute to it?

Homeostasis is the maintenance of a stable internal environment; negative feedback detects a deviation via receptors and coordinates effector responses that directly oppose the original change, restoring balance.

How does the body maintain water balance when dehydrated during physical activity?

The hypothalamus senses increased blood concentration and initiates thirst while releasing ADH; ADH instructs the kidneys to increase water reabsorption, reducing volume lost in urine.

How do viruses differ structurally and reproductively from bacteria?

Viruses are non-cellular entities requiring a host cell's machinery to multiply, whereas bacteria are single-celled cellular organisms capable of independent reproduction through binary fission.

What are five common routes of pathogen transmission?

Droplets (coughs/sneezes), contaminated food or water, direct physical contact, fomites (inanimate contaminated objects/surfaces), and vectors (living transmitters such as mosquitoes).

What are the roles of the body's first, second, and third lines of defence?

The first line provides physical and chemical barriers (skin, stomach acid, mucus); the second line provides non-specific innate responses (inflammation, fever, phagocytosis); the third line mounts adaptive specific responses using B cells (antibodies), T cells, and memory cells.

How do vaccines stimulate long-term immunity against pathogens?

Vaccines present a harmless form, antigen component, or genetic instructions of a pathogen, prompting an adaptive immune response and generating memory cells that react rapidly and aggressively upon subsequent exposures.

Why are antibiotics ineffective against viral illnesses, and how does antibiotic resistance arise?

Antibiotics inhibit bacterial cellular processes and have no impact on viruses; inappropriate or excessive antibiotic usage selects for surviving mutant bacteria that proliferate into resistant strains.

What is the defining distinction between infectious and non-infectious diseases?

Infectious diseases are transmissible conditions caused by pathogens (e.g., mumps, influenza), whereas non-infectious diseases cannot be transmitted between individuals and stem from genetics, lifestyle, or nutritional deficiencies (e.g., anaemia).

In scientific investigations, what are the independent, dependent, and controlled variables?

The independent variable is the condition deliberately altered, the dependent variable is the measurable result or response observed, and controlled variables are factors maintained unchanged to ensure valid testing.

What are gametes, gonads, and zygotes?

Gametes are haploid sex cells (sperm and ova), gonads are organs producing gametes and sex hormones (testes and ovaries), and a zygote is the single diploid cell resulting from fertilisation.

What are the roles of the scrotum, Fallopian tube, and prostate gland?

The scrotum maintains testes at temperatures below core body heat; Fallopian tubes carry eggs to the uterus and serve as the typical site of fertilisation; the prostate secretes protective and nutritive fluid into semen.

What advantages are offered by internal fertilisation compared to external fertilisation?

Internal fertilisation increases the success rate of gamete union, shields gametes and embryos against desiccation and environmental hazards, and requires fewer gametes to achieve successful reproduction.

What are the key hormonal roles of FSH, oestrogen, LH, and progesterone in the menstrual cycle?

FSH stimulates follicle and egg maturation; rising oestrogen rebuilds the endometrium; an LH surge triggers ovulation; and progesterone from the corpus luteum maintains the thickened uterine wall.