Biology (Cambridge 0610 IGCSE) Flashcards
Magnification
Cells are usually a few MICROMETERS (μm) long. 1μm = 1x10⁻⁶. Convert μm to mm by dividing by 1000.
MAGNIFICATION = image size ÷ object (cell) size
Cell biology
EUKARYOTIC CELLS
e.g. ANIMAL or PLANT cells
- Cell membrane (semi-permeable, controls what enters & leaves).
- nucleus (DNA)
- plant cells have a CELL WALL made from cellulose
- cytoplasm is the liquid that makes up the cell, in which most chemical reactions take place
- mitochondria is where aerobic respiration takes place, and makes energy for the cells
- ribosomes is where proteins are synthesised
- plants have CHLOROPLASTS (which contains chlorophyll, where photosynthesis takes place).
- plant cells also have a permanent vacuole (in which sap is stored).
PROKARYIOTIC CELLS
e.g. BACTERIA
- plasmid (loop of DNA)
- ribosomes
- mitochondria
Diffusion, osmosis & active transport
DIFFUSION is the movement of particles from an area of HIGH CONCENTRATION to that of a LOW CONCENTRATION (“down the concentration GRADIENT”). This is PASSIVE as it requires no energy. The RATE can be increased by increasing:
- the difference in concentrations
- surface area
- temperature
OSMOSIS is the diffusion of water across a SEMI-PERMEABLE MEMBRANE to balance the concentrations of solution inside and outside a cell. Water must move, as larger molecules cannot fit through the holes. Water moves IN if the concentration is higher OUTSIDE.
OSMOSIS PRACTICAL
- Weigh, and place identical cylinders from same vegetable in sugar solutions of varying concentrations,
- After set time, remove excesss water and reweigh, calculate % change in mass = final mass - initial mass ÷ initial mass x100.
ACTIVE TRANSPORT is the movement of particles through a membrane via CARRIER PROTEINS. This requires energy, and so can move them AGAINST the concentration gradient.
Organisation
- CELLS are the basic structural and functional unit of a living organism.
- TISSUE is a group of cells with similar structures working together to perform a specific function.
- ORGAN is a structure made up of a group of tissues working together to perform specific functions.
- ORGANISM is a living thing that carries out all the basic life processes.
Digestive system
- INGESTION: food enters mouth. Teeth break down food PHYSICALLY/MECHANICALLY. Salvia contains AMYLASE (an ENZYME)
- The LIVER produces BILE, which is stored in the GALL BLADDER before going to the small intestine. Bile EMULSIFIES LIPIDS to form droplets, increasing their surface area.
- The STOMACH contains HYDROCHLORIC ACID & ENZYMES that chemically digests food
- The PANCREAS secretes AMYLASE which breaks down STARCH into GLUCOSE in the small intestine
- WATER is absorbed into the bloodstream in the LARGE INTESTINE
- NUTRIENTS like glucose are absorbed into the bloodstream by the VILLI in the SMALL INTESTINE (starch is too large)
- EXCRETION/EGESTION: waste is ejected through the anus.
Assimilation
the movement of nutrients into cells
Enzymes
Enzymes are special PROTEINS that act as BIOLOGICAL CATALYSTS, often breaking down molecules into shorter ones (polymers into monomers).
They are SPECIFIC so only break down SUBSTRATES that fit their ACTIVE SITE (‘lock and key’ principle)
ACTIVITY (rate of reaction) increases with temperature until the enzymes DENATURES (active site changes shape). The same is true for too high or low pH
CARBOHYDRASES break dwon CARBOHYDRATES into simple sugars (e.g. AMYLASE breaks down STARCH into GLUCOSE)
PROTEASE break down PROTEINS into amino acids.
LIPASES break down LIPIDS into GLYCEROL & FATTY ACIDS.
Food tests
- STARCH - turns IODINE from ORANGE to BLACK
- SUGARS - turn BENEDICT’S SOLUTION from BLUE to GREEN/YELLOW to ORANGE to BRICK-RED
- PROTEIN - turns BIURETS’S REAGENT from BLUE to PURPLE
- LIPIDS (FATS) turn COLD ETHANOL CLOUDY
Diet & nutrition
-
CARBOHYDRATES
- SOURCE: bread, cereal, pasta, potatoes
- NEEDED FOR: respiration to release energy
-
FATS & OILS (lipids)
- SOURCE: butter, nuts
- NEEDED FOR: store of energy
-
PROTEIN
- SOURCE: meat, eggs, nuts
- NEEDED FOR: growth & repair
-
VITAMINS & MINERALS
- SOURCE: fruit, vegetables
- NEEDED FOR: various functions; vitamin C deficiency: scurvy
vitamin D for muscles & bones (rickets) calcium for bones, iron for blood.
-
fibre
- SOURCE: cereal, bread, vegetables, fruits
- NEEDED FOR: healthy digestive system.
Gas exchange in humans
Gas exchange in humans happens in the ALVEOLI of the LUNGS, which are specially adapted to make diffusion of gases efficient. The ALVEOLI provide a LARGE SURFACE AREA, are surrounded by CAPILLARIES for a GOOD BLOOD SUPPLY, have THIN WALLS (one cell thick) for short diffusion distance, and are kept VENTILATED with air through BREATHING to maintain a STEEP CONCENTRATION GRADIENT for OXYGEN and CARBON DIOXIDE.
The human BREATHING SYSTEM includes the LUNGS, which are the main organs of gas exchange, and several supporting structures. The DIAPHRAGM is a dome-shaped muscle at the bottom of the THORAX that helps change LUNG VOLUME. The RIBS form the RIBCAGE, which protects the LUNGS, and between them are INTERCOSTAL MUSCLES (EXTERNAL and INTERNAL), which move the RIBCAGE during BREATHING. Air enters through the LARYNX (voice box), passes through the TRACHEA (windpipe, which is held open by C-SHAPED RINGS of CARTILAGE), then through the BRONCHI, which branch into BRONCHIOLES, ending in tiny air sacs called ALVEOLI, surrounded by a network of CAPILLARIES where GAS EXCHANGE occurs.
To investigate GAS EXCHANGE, LIMEWATER can be used: it turns CLOUDY in the presence of CARBON DIOXIDE, so if a person breathes out through a tube into LIMEWATER, the change shows that EXPIRED AIR CONTAINS MORE CO₂ than INSPIRED AIR.
The COMPOSITION OF INSPIRED VS EXPIRED AIR differs:
INSPIRED AIR has MORE OXYGEN, LESS CARBON DIOXIDE, and LESS WATER VAPOUR.
EXPIRED AIR has LESS OXYGEN (used in RESPIRATION), MORE CARBON DIOXIDE (produced in RESPIRATION), and MORE WATER VAPOUR.
PHYSICAL ACTIVITY increases the RATE AND DEPTH OF BREATHING. This is because ACTIVE MUSCLES produce MORE CARBON DIOXIDE. The BRAIN DETECTS THIS INCREASE and signals the BREATHING MUSCLES to work FASTER AND DEEPER to remove CO₂ and take in MORE OXYGEN.
In the BREATHING SYSTEM, GOBLET CELLS produce MUCUS, which traps DUST and PATHOGENS. CILIATED CELLS have hair-like structures that SWEEP THE MUCUS OUT of the LUNGS. This helps protect the LUNGS from INFECTIONS and BLOCKAGES.
During BREATHING, the EXTERNAL INTERCOSTAL MUSCLES and DIAPHRAGM CONTRACT to pull the RIBCAGE UP AND OUT and FLATTEN the DIAPHRAGM, increasing THORACIC VOLUME and decreasing PRESSURE, drawing AIR IN (INHALATION). The INTERNAL INTERCOSTAL MUSCLES help pull the RIBS DOWN AND IN during FORCED EXHALATION, reducing VOLUME and pushing AIR OUT. These coordinated movements ensure EFFECTIVE VENTILATION of the LUNGS.
Circulatory system and the heart
The CIRCULATORY SYSTEM is made of BLOOD VESSELS, the HEART (a PUMP), and VALVES that maintain ONE-WAY BLOOD FLOW. It transports OXYGEN, CARBON DIOXIDE, NUTRIENTS, WASTE, HORMONES, and HEAT around the body.
- SINGLE CIRCULATION (FISH): Blood passes through the HEART ONCE per cycle.
- DOUBLE CIRCULATION (MAMMALS): Blood passes through the HEART TWICE — once through the LUNGS (PULMONARY) and once through the BODY (SYSTEMIC). This keeps OXYGENATED and DEOXYGENATED BLOOD separate and improves efficiency.
The HEART has FOUR CHAMBERS: LEFT and RIGHT ATRIA (upper), and LEFT and RIGHT VENTRICLES (lower). The SEPTUM separates OXYGENATED from DEOXYGENATED BLOOD. VALVES (ATRIOVENTRICULAR and SEMILUNAR) prevent backflow.
- LEFT VENTRICLE has a THICKER MUSCLE WALL than the RIGHT — it pumps to the whole body.
- ATRIA have THINNER WALLS than VENTRICLES — they only pump to the next chamber.
- The CORONARY ARTERIES supply the heart muscle with OXYGENATED BLOOD.
HEART FUNCTIONING:
- ATRIA CONTRACT → push blood to VENTRICLES.
- VENTRICLES CONTRACT → push blood to ARTERIES.
- VALVES open/close to ensure ONE-WAY FLOW.
MONITORING HEART ACTIVITY: ECG, PULSE RATE, and HEART SOUNDS (valves closing).
PHYSICAL ACTIVITY:
- Increases HEART RATE due to higher CARBON DIOXIDE in the blood.
- The BRAIN detects this and signals the HEART to beat faster and more forcefully.
- CORONARY HEART DISEASE:
- Caused by BLOCKED CORONARY ARTERIES (fat deposits).
- RISK FACTORS: POOR DIET, LACK OF EXERCISE, STRESS, SMOKING, GENETICS, AGE, SEX.
- PREVENTION: HEALTHY DIET and REGULAR EXERCISE reduce risk.
Blood
BLOOD is made up of PLASMA, RED BLOOD CELLS, WHITE BLOOD CELLS, and PLATELETS. PLASMA is the liquid part and transports BLOOD CELLS, IONS, NUTRIENTS (like glucose), UREA, HORMONES, and CARBON DIOXIDE. RED BLOOD CELLS transport OXYGEN using HAEMOGLOBIN, a red pigment that binds to oxygen in the lungs and releases it in tissues. These cells have no nucleus and are biconcave for a larger surface area. WHITE BLOOD CELLS defend against disease. There are two types:
- PHAGOCYTES, which ENGULF PATHOGENS in PHAGOCYTOSIS.
- LYMPHOCYTES, which produce ANTIBODIES to attack specific pathogens.
PLATELETS are fragments of cells involved in CLOTTING. They help prevent BLOOD LOSS and stop PATHOGENS from entering through wounds. CLOTTING happens when the protein FIBRINOGEN is converted into FIBRIN, which forms a MESH that traps blood cells to form a clot.
Blood vessels
There are three main types of BLOOD VESSELS: ARTERIES, VEINS, and CAPILLARIES. ARTERIES carry blood AWAY FROM THE HEART under HIGH PRESSURE, so they have THICK, ELASTIC WALLS and a NARROW LUMEN. VEINS carry blood BACK TO THE HEART under LOW PRESSURE and have THINNER WALLS, a WIDER LUMEN, and VALVES to prevent backflow. CAPILLARIES are the smallest vessels with VERY THIN WALLS (one cell thick), allowing efficient DIFFUSION of substances like oxygen, carbon dioxide, and nutrients.
Key blood vessels include:
- TO AND FROM THE HEART: AORTA (from heart to body), VENA CAVA (from body to heart), PULMONARY ARTERY (from heart to lungs), and PULMONARY VEIN (from lungs to heart).
- TO AND FROM THE LUNGS: PULMONARY ARTERY and PULMONARY VEIN.
- TO AND FROM THE KIDNEYS: RENAL ARTERY and RENAL VEIN.
- TO AND FROM THE LIVER: HEPATIC ARTERY, HEPATIC VEINS, and HEPATIC PORTAL VEIN.
The structure of these vessels is closely related to their function. ARTERIES must withstand and maintain high pressure, hence thick walls. VEINS carry blood at low pressure and need VALVES to stop backflow. CAPILLARIES are designed for exchange, so they have thin walls, a narrow lumen, and pass close to cells.
Photosynthesis
PHOTOSYNTHESIS is the process by which GREEN PLANTS make CARBOHYDRATES (mainly GLUCOSE) from CARBON DIOXIDE and WATER using LIGHT ENERGY, which is absorbed by CHLOROPHYLL. This takes place in the CHLOROPLASTS of leaf cells.
CHLOROPHYLL is a GREEN PIGMENT that captures LIGHT ENERGY and converts it into CHEMICAL ENERGY used to synthesise carbohydrates.
WORD EQUATION:
CARBON DIOXIDE + WATER → GLUCOSE + OXYGEN (in the presence of LIGHT and CHLOROPHYLL)
BALANCED CHEMICAL EQUATION:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
The GLUCOSE produced is used in several ways:
Converted to STARCH for STORAGE.
Used to make CELLULOSE for CELL WALLS.
Used in RESPIRATION to release ENERGY.
Changed into SUCROSE for TRANSPORT in the PHLOEM.
Used to make NECTAR to attract pollinators.
MINERAL IONS needed:
NITRATE IONS to make AMINO ACIDS (for proteins).
MAGNESIUM IONS to make CHLOROPHYLL.
EXPERIMENTS:
Use destarched leaves and iodine to test for STARCH.
Remove light, CO₂, or chlorophyll to test their necessity (with controls).
Measure the effect of LIGHT INTENSITY, CARBON DIOXIDE LEVEL, and TEMPERATURE on PHOTOSYNTHESIS RATE (e.g. bubble counting or oxygen volume).
Use HYDROGENCARBONATE INDICATOR with aquatic plants to show gas exchange:
YELLOW = HIGH CO₂ (dark)
ORANGE = NORMAL CO₂
PURPLE = LOW CO₂ (photosynthesis occurring)
LIMITING FACTORS of photosynthesis:
LIGHT INTENSITY, CO₂ CONCENTRATION, and TEMPERATURE all affect the RATE. The one in shortest supply limits the process.
Leaf structure
LEAVES are specially adapted for PHOTOSYNTHESIS. Most are BROAD (large surface area) and THIN, allowing more light absorption and efficient gas exchange.
STRUCTURES AND FUNCTIONS:
UPPER EPIDERMIS: Transparent and protective, allows light through.
CUTICLE: Waxy layer reducing water loss.
PALISADE MESOPHYLL: Packed with CHLOROPLASTS, main site of PHOTOSYNTHESIS.
SPONGY MESOPHYLL: Loosely packed cells with AIR SPACES for gas diffusion.
STOMATA: Pores in the LOWER EPIDERMIS that allow gas exchange (CO₂ in, O₂ out).
GUARD CELLS: Control the opening and closing of STOMATA.
XYLEM: Transports WATER and MINERALS from the roots to the leaf. TRASPIRATION (unidirectional) upwards.
PHLOEM: Transports SUGARS (like SUCROSE) from the leaf to the rest of the plant. TRANSLOCATION (bidirectional)
These structural adaptations make leaves efficient in absorbing LIGHT and CO₂, transporting materials, and minimising water loss — all essential for effective PHOTOSYNTHESIS.
Flower strucutre & reproduction
In SEXUAL REPRODUCTION in plants, specialized structures in FLOWERS are used to produce male and female gametes and to ensure pollination and fertilisation.
An INSECT-POLLINATED FLOWER contains:
SEPALS: Protect the bud before it opens.
PETALS: Often brightly coloured and scented to attract insects.
STAMENS (male part): Made up of FILAMENTS (stalks) and ANTHERS, which produce POLLEN GRAINS (the male gametes).
CARPELS (female part): Consist of STIGMA (where pollen lands), STYLE (supports the stigma), and OVARY, which contains OVULES (female gametes).
In contrast, WIND-POLLINATED FLOWERS have:
LARGE, EXPOSED STIGMAS to catch airborne pollen.
LONG FILAMENTS so anthers hang outside the flower, aiding pollen release.
They usually have SMALL, DULL PETALS and NO SCENT or NECTAR.
POLLEN GRAINS differ between types:
INSECT-POLLINATED: Larger, spiky or sticky to attach to insects.
WIND-POLLINATED: Smaller, smooth, and produced in large numbers for easier dispersal by air.
POLLINATION is the transfer of POLLEN from the ANTHER to the STIGMA.
SELF-POLLINATION happens within the SAME FLOWER or SAME PLANT.
CROSS-POLLINATION occurs between DIFFERENT PLANTS of the SAME SPECIES.
Self-pollination leads to LESS VARIATION in offspring, making the population LESS ABLE TO ADAPT to changes. Cross-pollination introduces MORE GENETIC VARIATION, which can improve survival but depends on the presence of POLLINATORS like insects or wind.
Fertilisation and germination
FERTILISATION occurs when the NUCLEUS OF A POLLEN GRAIN fuses with the NUCLEUS OF AN OVULE, forming a ZYGOTE.
After pollination, a POLLEN TUBE grows from the pollen grain down the STYLE into the OVARY, and into an OVULE. The male nucleus then travels down the tube and fuses with the female nucleus to complete fertilisation.
GERMINATION is the process by which a seed begins to grow into a new plant. For successful germination, a seed needs:
WATER to activate enzymes and swell the seed.
OXYGEN for AEROBIC RESPIRATION.
A SUITABLE TEMPERATURE for enzyme activity.
These factors can be tested by experiments using different environmental setups to observe which conditions allow seeds to sprout.
Translocation
TRANSLOCATION is the movement of SUCROSE and AMINO ACIDS through the PHLOEM from SOURCES (where they are made or released) to SINKS (where they are used or stored). This process is essential for transporting products of photosynthesis and other nutrients throughout the plant.
SOURCES are regions in the plant that PRODUCE or RELEASE sucrose and amino acids into the phloem. Examples include LEAVES during photosynthesis or STORAGE ORGANS (like tubers) when they are mobilising food.
SINKS are areas where these substances are USED for GROWTH or STORAGE, such as ROOTS, DEVELOPING FRUITS, SEEDS, or YOUNG LEAVES.
Some plant parts can switch roles:
A LEAF is a SOURCE when it’s photosynthesising but may act as a SINK when it’s young and still developing.
A ROOT may act as a SINK when storing sucrose, but in early spring, it can become a SOURCE, releasing stored nutrients to support new growth.
Transpiration
TRANSPIRATION is the process by which WATER VAPOUR is lost from plant leaves, primarily through the STOMATA. This process plays a key role in WATER AND NUTRIENT TRANSPORT throughout the plant.
Water Evaporation: Water evaporates from the MESOPHYLL CELLS into the AIR SPACES inside the leaf, then diffuses out through the STOMATA as WATER VAPOUR. This creates a TRANSPIRATION STREAM, drawing water from the roots to the leaves.
Factors Affecting Transpiration Rate:
Temperature: High temperatures increase the rate of transpiration by increasing the evaporation of water from leaf surfaces.
Wind Speed: Strong winds increase transpiration by removing water vapour from around the stomata, maintaining a concentration gradient.
Humidity: Lower humidity increases transpiration as the difference between the moisture inside the leaf and the air outside is greater.
Water Movement in Plants:
Water moves UPWARDS THROUGH THE XYLEM by a process known as TRANSPIRATION PULL. The loss of water from the stomata creates a suction effect that draws a column of water from the roots to the leaves.
FORCES OF ATTRACTION between water molecules (cohesion) and between water and xylem walls (adhesion) help maintain this upward flow.
Wilting: Wilting occurs when the plant loses more water than it can take up, causing TURGIDITY to decrease and the plant to lose structural support. This is usually due to excessive WATER LOSS from transpiration, especially when there is not enough water available in the soil.
Characteristics of living organisms
Living organisms share seven KEY CHARACTERISTICS:
MOVEMENT: The ability to change position or place, either as an entire organism or parts of it.
RESPIRATION: The series of CHEMICAL REACTIONS that break down nutrient molecules to release energy, vital for metabolism.
SENSITIVITY: The ability to DETECT AND RESPOND to changes in both internal and external environments.
GROWTH: The permanent INCREASE in size and mass due to cell division and expansion.
REPRODUCTION: The ability to produce offspring to continue the species.
EXCRETION: The removal of WASTE PRODUCTS and excess substances produced by metabolism.
NUTRITION: The process of taking in materials (like food) for ENERGY, GROWTH, and development.
Classification system
Organisms are grouped based on SHARED FEATURES, and SPECIES are defined as organisms that can reproduce to produce fertile offspring.
The BINOMIAL SYSTEM is a naming system for species, where the GENUS and SPECIES are used to uniquely identify organisms.
DICHOTOMOUS KEYS are tools that help classify organisms by narrowing down features step-by-step.
Evolutionary Relationships: Classification aims to reflect evolutionary history, and DNA SEQUENCES are used to classify organisms. Those with a MORE RECENT COMMON ANCESTOR have more similar BASE SEQUENCES in their DNA than those with a more distant ancestor.
Features of organism
Organisms can be classified into KINGDOMS (Animal, Plant, Fungi, Prokaryotes, Protoctists) based on distinct features.
Animal Kingdom: Grouped into VERTEBRATES (mammals, birds, reptiles, amphibians, fish) and ARTHROPODS (myriapods, insects, arachnids, crustaceans).
Plant Kingdom: Grouped into FERNS and FLOWERING PLANTS (dicotyledons and monocotyledons).
Viruses are not classified as living organisms but have a PROTEIN COAT and GENETIC MATERIAL.
Cell structure
Plant Cells: Have a CELL WALL, CHLOROPLASTS, VACUOLES, and all other typical organelles like the NUCLEUS, CYTOPLASM, CELL MEMBRANE, RIBOSOMES, and MITOCHONDRIA.
Animal Cells: Lack a CELL WALL and CHLOROPLASTS but have similar structures like NUCLEUS, CYTOPLASM, CELL MEMBRANE, RIBOSOMES, and MITOCHONDRIA.
Bacterial Cells: Include a CELL WALL, CELL MEMBRANE, CYTOPLASM, RIBOSOMES, CIRCULAR DNA, and PLASMIDS, but no nucleus or organelles like mitochondria.
Specialised Cells have unique structures to perform specific functions:
CILIATED CELLS move mucus in airways.
ROOT HAIR CELLS absorb water and nutrients.
PALISADE MESOPHYLL CELLS carry out photosynthesis.
NEURONES transmit electrical signals.
RED BLOOD CELLS carry oxygen via haemoglobin.
SPERM AND EGG CELLS (GAMETES) are involved in reproduction.
Hierarchy of Organisation: Cells form TISSUES, tissues form ORGANS, organs form ORGAN SYSTEMS, and organ systems work together to form an ORGANISM.
Active transport
Active Transport is the MOVEMENT OF PARTICLES across a cell membrane from a region of LOWER CONCENTRATION to a region of HIGHER CONCENTRATION, which is against the concentration gradient. This process requires ENERGY from RESPIRATION.
Protein Carriers facilitate the movement of molecules or ions during active transport, helping them pass through the membrane.
Importance: Active transport is essential for processes like ION UPTAKE by ROOT HAIRS in plants and other cellular functions where substances need to be concentrated in areas against their natural gradient.
