Science CT3 - Plant and Human Organ Systems.

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Root Function

Anchors the plant in the soil and absorbs water and mineral ions.

Stem Function

Supports the leaves, flowers, and fruits, and transports substances between the roots and leaves.

Leaf Function

The main site of photosynthesis; converts light energy into chemical energy (glucose).

Flower Function

The reproductive organ of the plant; responsible for producing seeds through pollination and fertilisation.

Waxy Cuticle (Leaf Tissue)

A transparent, waterproof layer on the upper epidermis that reduces water loss by evaporation.

Upper Epidermis (Leaf Tissue)

A single layer of transparent cells that protects the inner leaf and allows light to pass through to the palisade layer.

Palisade Mesophyll (Leaf Tissue)

A layer of tightly packed, column-shaped cells containing many chloroplasts; the primary site of photosynthesis.

Spongy Mesophyll (Leaf Tissue)

A layer of loosely packed, irregularly shaped cells with air spaces between them to allow for gas exchange (CO₂ and O₂ diffusion).

Guard Cells (Leaf Tissue)

A pair of sausage-shaped cells that surround a stoma; they control the opening and closing of the stomata for gas exchange.

Stomata (Leaf Tissue)

Small pores, usually on the lower epidermis, that allow carbon dioxide to enter and oxygen and water vapour to exit the leaf.

Word Equation for Photosynthesis

Carbon Dioxide + Water → Glucose + Oxygen (in the presence of light and chlorophyll)

Uses of Glucose: Respiration

Used directly in respiration to release energy for growth, repair, and other life processes.

Uses of Glucose: Starch Storage

Converted into insoluble starch for long-term energy storage, which doesn't affect the osmotic balance of cells.

Uses of Glucose: Cellulose

Converted into cellulose to build and strengthen cell walls.

Uses of Glucose: Sucrose Transport

Converted into sucrose for transport via the phloem to other parts of the plant.

Uses of Glucose: Amino Acids & Proteins

Combined with nitrate ions from the soil to form amino acids, which are then built into proteins for growth.

Testing a Leaf for Starch (Method)

1. Boil leaf in water (to kill it). 2. Boil in ethanol in a hot water bath (to remove chlorophyll). 3. Rinse in cold water (to soften). 4. Add iodine solution. A blue-black colour indicates starch is present.

Why Ethanol Must Be Heated in a Water Bath

Because ethanol is highly flammable and cannot be heated directly with a Bunsen burner.

Light Intensity as a Limiting Factor

As light intensity increases, the rate of photosynthesis increases, until another factor (like CO₂ or temperature) becomes limiting.

CO₂ Concentration as a Limiting Factor

As CO₂ concentration increases, the rate of photosynthesis increases, until another factor (like light intensity) becomes limiting.

How Reactants Move into a Leaf

Water enters root hair cells by osmosis and is transported up the xylem. Carbon dioxide diffuses into the leaf through the stomata.

How Products Move out of a Leaf

Oxygen diffuses out of the leaf through the stomata, from a high concentration inside to a low concentration in the air.

Xylem Function

Transports water and dissolved mineral ions from the roots up to the stem and leaves in a one-way flow. Walls are strengthened with lignin.

Phloem Function

Transports sucrose and amino acids up and down the plant from sources (leaves) to sinks (growing tips, roots, fruits).

Definition of Transpiration

The loss of water vapour from the aerial parts of a plant (mainly through the stomata in the leaves).

Impact of Nitrate Deficiency

Plants show stunted growth and older leaves turn yellow, as nitrates are needed to make proteins and chlorophyll.

Impact of Magnesium Deficiency

Leaves turn yellow (chlorosis) because magnesium is needed to make chlorophyll.

Petal Function

Often brightly coloured to attract insect pollinators.

Sepal Function

Green, leaf-like structures that protect the flower bud before it opens.

Anther Function

The male part of the flower that produces and releases pollen grains.

Filament Function

The stalk that supports the anther, holding it up for pollinators or wind.

Stigma Function

The female part, often sticky, that receives pollen grains during pollination.

Style Function

The stalk that connects the stigma to the ovary, through which a pollen tube grows.

Ovary Function

Contains the female ovules and develops into the fruit after fertilisation.

Ovule Function

Contains the female gamete (egg cell) and develops into a seed after fertilisation.

Self-Pollination

The transfer of pollen from an anther to the stigma of the same flower or the same plant.

Cross-Pollination

The transfer of pollen from an anther of one plant to the stigma of a flower on a different plant of the same species.

Role of Wind in Pollination

Carries lightweight pollen grains from one plant to another, often over long distances; no energy required to produce petals or nectar.

Role of Animals in Pollination

Animals (e.g. insects, birds) visit flowers for nectar, inadvertently carrying sticky/spiky pollen grains to the next flower they visit.

Features of Wind-Pollinated Flowers

Dull/no petals, no scent/nectar, large anthers hanging outside, feathery stigma, small/light pollen grains produced in large quantities.

Features of Insect-Pollinated Flowers

Brightly coloured petals, scented with nectar, anthers and stigma enclosed inside, sticky/spiky pollen grains.

Changes after Pollination: Fertilisation

The male nucleus from the pollen grain fuses with the female nucleus in the ovule to form a zygote.

Changes after Pollination: Seed & Fruit

The zygote develops into an embryo plant (seed). The ovule develops into the seed. The ovary wall develops into the fruit.

Seed Dispersal: Wind

Fruits/seeds are lightweight or have "wings" or "parachutes" (e.g. sycamore, dandelion).

Seed Dispersal: Animals

Fruits are fleshy and eaten (seeds pass out in droppings), or seeds have hooks to stick to fur (e.g. burdock).

Seed Dispersal: Self/Mechanical

The fruit dries and splits open with force, flicking seeds out (e.g. pea pods).

Benefits of Seed Dispersal

Reduces competition for light, water, and nutrients with the parent plant and siblings; helps the species colonise new areas.

Seed Coat (Testa) Function

A tough, protective outer layer that protects the embryo from damage and infection.

Radicle Function

The embryonic root; it is the first part to grow out of the seed, growing downwards to anchor the plant and absorb water.

Plumule Function

The embryonic shoot; it grows upwards after the radicle and develops into the stem and first true leaves.

Cotyledon Function

Food stores for the embryo, providing starch and proteins for energy and growth until the seedling can photosynthesise.

Conditions for Germination

Water (to activate enzymes and soften the testa), Oxygen (for aerobic respiration), and a suitable Warmth/Temperature (for enzyme action).

Comparing Inhaled vs. Exhaled Air (Composition)

Inhaled air has more oxygen (21%) and very little carbon dioxide (0.04%). Exhaled air has less oxygen (16%) and more carbon dioxide (4%).

Comparing Inhaled vs. Exhaled Air (Temperature)

Exhaled air is generally warmer than inhaled air, as it has been heated by the body.

Nasal Cavity Function

Warms, moistens, and filters incoming air; contains hairs and mucus to trap dust and pathogens.

Trachea (Windpipe) Function

The main airway reinforced by C-shaped cartilage rings to keep it open; carries air to the bronchi.

Bronchus (Plural: Bronchi) Function

Two branches of the trachea that carry air into each lung.

Bronchioles Function

Smaller, finer branches inside the lung that carry air to the alveoli; contain smooth muscle.

Alveoli (Singular: Alveolus) Function

Tiny air sacs at the end of bronchioles where gas exchange occurs. They provide a large, moist surface area.

Diaphragm Function

A large, dome-shaped sheet of muscle separating the chest cavity from the abdomen; its movement controls breathing.

Intercostal Muscles Function

Muscles located between the ribs that move the ribcage up and out (inhalation) or down and in (exhalation).

Process of Inhalation (Breathing In)

Intercostal muscles contract, ribcage moves up and out. Diaphragm contracts and flattens. Volume of thorax increases, pressure decreases, so air is drawn in.

Process of Exhalation (Breathing Out)

Intercostal muscles relax, ribcage moves down and in. Diaphragm relaxes and domes up. Volume of thorax decreases, pressure increases, so air is pushed out.

Gas Exchange in Alveoli

Oxygen diffuses from the alveoli (high concentration) into the blood (low concentration). Carbon dioxide diffuses from the blood (high concentration) into the alveoli (low concentration).

Role of Ciliated Epithelium

Lines the trachea and bronchi. Goblet cells secrete mucus to trap dust/microbes. Cilia are tiny hairs that beat in a wave-like motion to move this mucus up towards the throat to be swallowed.

Effects of Smoking/Vaping on Lungs

Damages cilia, causing mucus build-up leading to smoker's cough. Causes chronic bronchitis and emphysema (breakdown of alveoli walls, reducing surface area for gas exchange). Contains carcinogens increasing lung cancer risk.

Effect of Asthma on Lungs

The walls of the airways become inflamed and swollen, and the muscles around the bronchioles contract, narrowing the airways and making it difficult to breathe.

Effect of High Altitude on Lungs

Air pressure is lower, so there are fewer oxygen molecules per breath. To compensate, the body increases breathing rate and depth, and produces more red blood cells to carry oxygen more efficiently.

Where Blood Becomes Oxygenated

In the alveoli (capillaries surrounding the air sacs) of the lungs.

Where Blood Becomes Deoxygenated

In the body's tissues (capillaries in organs/muscles), where oxygen diffuses into cells for respiration.

Right Atrium Function

Receives deoxygenated blood from the body via the vena cavae.

Right Ventricle Function

Pumps deoxygenated blood to the lungs via the pulmonary artery.

Left Atrium Function

Receives oxygenated blood from the lungs via the pulmonary veins.

Left Ventricle Function

Pumps oxygenated blood to the body via the aorta; has a very thick muscular wall to generate high pressure.

Septum Function

The thick muscular wall separating the left and right sides of the heart, preventing oxygenated and deoxygenated blood from mixing.

Valves Function

Flaps of tissue that prevent the backflow of blood, ensuring it flows in one direction through the heart.

Aorta Function

The main artery carrying oxygenated blood from the left ventricle to the body.

Pulmonary Artery Function

The artery carrying deoxygenated blood from the right ventricle to the lungs.

Pulmonary Vein Function

The vein carrying oxygenated blood from the lungs to the left atrium.

Vena Cavae Function

The large veins carrying deoxygenated blood from the body to the right atrium.

Causes of Heart Attacks

Blockage of the coronary arteries (usually by a blood clot forming on a fatty plaque of cholesterol). This deprives the heart muscle of oxygen and glucose, causing cells to die.

Red Blood Cell Function

Contains haemoglobin to bind and transport oxygen around the body. No nucleus to maximise space for oxygen.

White Blood Cell Function

Part of the immune system; fights infection by producing antibodies or engulfing pathogens (phagocytosis).

Platelet Function

Small cell fragments involved in blood clotting at sites of injury.

Plasma Function

The liquid component of blood; transports blood cells, dissolved nutrients (glucose, amino acids), hormones, carbon dioxide, and waste products.

Artery (Structure)

Thick, muscular, elastic wall to withstand high pressure. Small lumen. Carries blood away from the heart (no valves).

Vein (Structure)

Thin wall with little muscle. Large lumen. Contains valves to prevent backflow. Carries blood towards the heart.

Capillary (Structure)

Wall is a single cell thick (endothelium). Very small lumen. Links arteries to veins; site of gas and nutrient exchange by diffusion.