biology p1

Structural characteristics of eukaryotic cells

Cells that contain a cell membrane, cytoplasm, and their genetic material (DNA) enclosed within a nucleus (e.g., plant and animal cells).

Structural characteristics of prokaryotic cells

Much smaller cells with cytoplasm and a cell membrane surrounded by a cell wall, containing genetic material as a single DNA loop not enclosed in a nucleus, alongside optional plasmids.

Plasmids

Small, circular rings of extra DNA found in bacterial cells that can replicate independently.

Measurement prefixes in standard form (centi, milli, micro, nano)

Centi ($\text{c}$) is $10^{-2}$, milli ($\text{m}$) is $10^{-3}$, micro ($\mu$) is $10^{-6}$, and nano ($\text{n}$) is $10^{-9}$.

Order of magnitude comparison principle

A scale comparison using powers of 10, where a difference of 1 order of magnitude is $10^1$ ($10\times$) and 2 orders of magnitude is $10^2$ ($100\times$).

Sub-cellular role of the nucleus

Contains genetic material (DNA) organized into chromosomes and controls the chemical activities of the cell.

Sub-cellular role of the cytoplasm

A jelly-like fluid where most cellular chemical reactions take place, controlled by enzymes.

Sub-cellular role of the cell membrane

A partially permeable barrier that controls the movement of substances into and out of the cell.

Sub-cellular role of mitochondria

The site of aerobic cellular respiration, which releases energy for the cell.

Sub-cellular role of ribosomes

The site of protein synthesis in the cell.

Sub-cellular role of chloroplasts

Contain the green pigment chlorophyll to absorb light energy needed for photosynthesis.

Sub-cellular role of the permanent vacuole

A fluid-filled space containing cell sap that maintains turgor pressure to support plant cell structure.

Sub-cellular role of the cellulose cell wall

An outer layer made of cellulose fibres that strengthens and provides structural support to plant and algal cells.

Preparation of plant cells for light microscopy (Required Practical 1)

Peel a thin epidermal layer, lay it flat on a glass slide, add a drop of iodine stain, lower a coverslip at an angle to avoid air bubbles, and view under lowest power first before focusing.

Biological drawing rules under a light microscope (Required Practical 1)

Draw clear, continuous outlines without shading, draw straight horizontal label lines without arrowheads, and record the total magnification scale.

Structural adaptations of a sperm cell

Streamlined head and long flagellum for swimming, packed with mitochondria in the middle piece for energy, and carries acrosome enzymes to digest the egg coat.

Structural adaptations of a nerve cell (neurone)

Extended axon to transmit electrical impulses across long distances, branched dendrites to connect with other neurones, and an insulating myelin sheath to accelerate impulse speed.

Structural adaptations of a muscle cell

Contains specialized protein filaments that slide past each other to cause contraction, abundant mitochondria to release energy, and stores glycogen.

Structural adaptations of a root hair cell

A large surface area extension to accelerate water uptake by osmosis and mineral ions by active transport, with a large vacuole and no chloroplasts.

Structural adaptations of xylem tissue

Dead, hollow tubes with absent end walls allowing continuous movement of water and dissolved minerals, reinforced with lignin spirals for support.

Structural adaptations of phloem tissue

Elongated living cells with perforated end plates (sieve plates) allowing cell sap containing dissolved sugars to travel, supported by companion cells.

Timing of cell differentiation in animals versus plants

Most animal cells differentiate at an early developmental stage, whereas many plant cells retain the capacity to differentiate throughout their lifespan.

Role of cell division in mature animals

Primarily restricted to the repair and replacement of damaged or worn-out tissues.

Differences between magnification and resolution

Magnification indicates how many times larger an image appears compared to the real object; resolution is the ability to distinguish two separate points as distinct structures.

Advantages of electron microscopes over light microscopes

Much higher magnification and resolving power, allowing visualization of internal sub-cellular structures (such as ribosomes and mitochondrial cristae) in fine detail.

Formula for calculating magnification

$$\text{magnification} = \frac{\text{size of image}}{\text{size of real object}}$$

Organisation of chromosomes in human body cells

Composed of DNA molecules carrying numerous genes, typically arranged in $23$ homologous pairs ($46$ total chromosomes).

Three main stages of the cell cycle

Stage 1 (Interphase): cell grows, increases ribosomes and mitochondria, and replicates DNA; Stage 2 (Mitosis): chromosomes are pulled apart and the nucleus divides; Stage 3 (Cytokinesis): cytoplasm and cell membrane divide to form two identical cells.

Biological importance of mitosis

Essential for growth, development, and tissue repair in multicellular organisms by creating genetically identical daughter cells.

Definition of a stem cell

An undifferentiated cell capable of giving rise to many more identical cells of the same type, and from which certain specialised cell types arise via differentiation.

Potency differences between embryonic and adult bone marrow stem cells

Embryonic stem cells can differentiate into almost all human cell types; adult bone marrow stem cells can only differentiate into limited types, primarily blood cells.

Therapeutic cloning procedure and advantage

An embryo is produced with identical genetic material to the patient; stem cells harvested from it are not rejected by the patient's immune system.

Characteristics and applications of plant meristem stem cells

Found at root and shoot growing tips; retain differentiation capacity throughout life to clone rare species to prevent extinction or produce disease-resistant crops.

Risks and ethical objections to stem cell use

Risks include potential viral infection transfer and tumour development; ethical objections arise from treating viable human embryos as disposable material.

Definition of diffusion

The spreading out of particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.

Substances transported across mammalian cell membranes by diffusion

Oxygen and carbon dioxide during alveolar gas exchange, and the metabolic waste product urea moving from liver cells into blood plasma.

Three factors that accelerate the rate of diffusion

A steeper concentration gradient, higher temperature (providing more kinetic energy), and a larger surface area of the exchange membrane.

Surface area to volume ratio in single-celled versus multicellular organisms

Single-celled organisms possess a large surface area to volume ratio allowing sufficient diffusion across the surface; multicellular organisms possess a small ratio requiring specialized exchange surfaces.

Four structural adaptations of effective exchange surfaces

Large surface area, thin membrane providing a short diffusion path, rich blood supply to preserve steep concentration gradients, and active ventilation.

Definition of osmosis

The diffusion of water from a dilute solution to a concentrated solution across a partially permeable membrane.

Investigating osmosis in plant tissue (Required Practical 2)

Submerge equal-sized potato cylinders in varied sucrose solutions ($0.0$ to $1.0\,mol\,dm^{-3}$), dry them after a set time, reweigh, and plot percentage mass change to determine internal concentration.

Formula for percentage change in mass

$$\text{percentage change} = \frac{\text{final mass} - \text{initial mass}}{\text{initial mass}} \times 100$$

Definition of active transport

The movement of substances from a more dilute solution to a more concentrated solution (against a concentration gradient), requiring energy from cellular respiration.

Examples of active transport in plants and animals

Uptake of mineral ions from dilute soil solutions into plant root hairs, and absorption of glucose from the gut lumen into higher-concentration blood.

Hierarchical principles of biological organisation

Cells are basic building blocks; tissues are groups of cells with similar structure and function; organs are aggregations of tissues; organ systems coordinate organs to form organisms.

General function of digestive enzymes

Convert large insoluble food molecules into small, soluble molecules capable of being absorbed into the bloodstream.

Lock and key theory of enzyme action

The substrate possesses a complementary shape to the enzyme's active site, forming an enzyme-substrate complex that catalyses the reaction without altering the enzyme.

Mechanism of enzyme denaturation

Excess heat or unsuitable pH changes the shape of the active site, preventing the complementary substrate from fitting and halting catalytic activity.

Substrates, products, and production sites of amylase, protease, and lipase

Amylase (salivary glands, pancreas, small intestine) digests starch to simple sugars; Protease (stomach, pancreas, small intestine) digests proteins to amino acids; Lipase (pancreas, small intestine) digests lipids to glycerol and fatty acids.

Origin, storage, and functions of bile

Made in the liver and stored in the gall bladder; alkaline to neutralise stomach hydrochloric acid and emulsifies fats into droplets to enlarge the surface area for lipase.

Chemical reagents and positive results for food tests (Required Practical 3)

Starch: Iodine turns from orange-brown to blue-black; Reducing sugars: Heated Benedict's turns from blue to green/yellow/brick-red; Protein: Biuret reagent turns from blue to purple; Lipids: Ethanol forms a milky-white emulsion.

Continuous sampling method for pH effect on amylase (Required Practical 4)

Mix buffered amylase and starch at constant temperature, transfer drops into iodine wells every $30\,\text{seconds}$, and record the elapsed time until iodine ceases turning blue-black.

Functioning of the double circulatory system

The right ventricle pumps deoxygenated blood to the lungs for gas exchange, and the left ventricle pumps oxygenated blood at higher pressure around the body.

Four major blood vessels associated with the heart

Vena cava delivers deoxygenated blood to the right atrium; pulmonary artery sends blood to lungs; pulmonary vein returns oxygenated blood to left atrium; aorta distributes blood to body.

Control of natural resting heart rate

Controlled by a group of pacemaker cells located in the right atrium that emit regular electrical impulses; treated with an artificial electronic pacemaker if irregular.

Structural adaptations of arteries, veins, and capillaries

Arteries: thick elastic and muscular walls to withstand high pressure; Veins: thin walls, wide lumen, and valves to prevent backflow; Capillaries: walls one cell thick for short diffusion pathways.

Four components of blood and their functions

Plasma: transports dissolved nutrients, urea, and hormones; Red blood cells: contain haemoglobin to carry oxygen; White blood cells: defend against pathogens; Platelets: cell fragments triggering blood clotting.

Pathology of coronary heart disease (CHD)

Fatty materials accumulate inside coronary arteries, narrowing them, restricting blood flow, and depriving the heart muscle of oxygen.

Comparison of stents and statins for coronary heart disease

Stents: expandable metal mesh tubes keeping arteries patent (immediate relief, surgical infection risk); Statins: daily drugs reducing blood cholesterol (preventative, potential liver or muscle side effects).

Treatments for faulty heart valves and severe heart failure

Faulty valves are replaced with biological (donor tissue) or mechanical valves; end-stage heart failure is treated with a human heart transplant or temporary mechanical artificial heart.

Definition of health and disease interactions

A state of physical and mental well-being; immune deficiencies increase vulnerability to pathogens, persistent viral infections trigger cancers, and severe physical illness can provoke depression.

Proven lifestyle risk factors and associated non-communicable diseases

High fat diet and smoking link to cardiovascular disease; obesity links to Type 2 diabetes; alcohol links to liver cirrhosis and impaired brain function; smoking links to lung cancer.

Differences between benign and malignant tumours

Benign tumours are localized growths contained within a membrane that do not invade other tissues; malignant tumours are cancers that invade neighboring tissues and metastasize via blood to form secondary tumours.

Structural adaptations of leaf tissues

Epidermis is transparent with a waxy cuticle; palisade mesophyll is densely packed with chloroplasts near the light; spongy mesophyll has air spaces allowing gas diffusion.

Role of stomata and guard cells

Guard cells adjust their turgidity to open or close microscopic stomatal pores, regulating carbon dioxide entry and water vapour transpiration.

Definition of the transpiration stream

The upward movement of water and mineral ions through xylem vessels from the roots to the leaves, driven by water evaporation from stomata.

Four environmental factors that accelerate transpiration rate

Elevated temperature, increased light intensity, increased air movement (wind), and reduced atmospheric humidity.

Definition of translocation in phloem

The movement of dissolved sugars from photosynthetic leaves to growing or storage tissues through living phloem sieve tubes.

Definition and classification of pathogens

Microorganisms that cause infectious disease, classified into viruses, bacteria, protists, and fungi; spread by direct contact, water, or air.

Mechanisms by which bacteria and viruses cause disease

Bacteria reproduce rapidly and produce toxic chemicals that damage tissue; viruses invade host cells, reproduce inside them, and cause the cells to burst.

Symptoms, spread, and prevention of Measles, HIV, and TMV

Measles: fever and red rash spread by droplet inhalation, prevented by MMR vaccine; HIV: flu-like illness attacking immune cells, spread sexually or via shared needles; TMV: mosaic leaf discolouration reducing plant photosynthesis.

Symptoms, spread, and control of Salmonella and Gonorrhoea

Salmonella: fever, cramps, vomiting from ingested food toxins, controlled by poultry vaccination; Gonorrhoea: STD with yellow discharge and painful urination, prevented with condoms and treated with antibiotics.

Symptoms, transmission, and management of Rose black spot and Malaria

Rose black spot: fungal purple/black spots causing early leaf drop, spread by wind/water, treated with fungicides; Malaria: protist causing recurrent fevers, spread by mosquito vectors, controlled with nets and vector eradication.

Four non-specific human body defence systems

Skin forms an impermeable physical and sebum barrier; nasal hairs and mucus trap particles; trachea and bronchi produce mucus swept up by cilia; stomach produces hydrochloric acid.

Three defence mechanisms of white blood cells

Phagocytosis (engulfing and digesting pathogens), antibody production (neutralising specific complementary antigens), and antitoxin production (counteracting bacterial toxins).

Mechanism of vaccination

Introducing dead or inactive forms of a pathogen stimulates white blood cells to produce specific antibodies and memory cells, enabling rapid secondary immune responses.

Action of antibiotics versus painkillers

Antibiotics kill infective bacteria inside the human body without damaging body cells; painkillers alleviate symptoms without killing pathogens; antibiotics cannot kill viruses inside host cells.

Traditional plant and microbial origins of common medicines

Digitalis (heart medication) originates from foxgloves, aspirin (painkiller) originates from willow bark, and penicillin was discovered from Penicillium mould.

Three stages of preclinical and clinical drug testing

Preclinical: testing on cells, tissues, and live animals for toxicity and efficacy; Clinical phase 1: low doses on healthy volunteers for safety; Clinical phase 2/3: trials on patients to determine optimum dose.

Purpose of double-blind trials and placebos

Neither volunteers nor doctors know who receives the real medicine or an inactive placebo, eliminating psychological bias and establishing genuine efficacy.

Photosynthesis word equation, symbol equation, and reaction type

$\text{carbon dioxide} + \text{water} \rightarrow \text{glucose} + \text{oxygen}$; $6CO<em>2 + 6H</em>2O \rightarrow C<em>6H</em>{12}O<em>6 + 6O</em>2$; an endothermic reaction transferring light energy to chloroplasts.

Four factors limiting the rate of photosynthesis

Light intensity, carbon dioxide concentration, ambient temperature, and amount of chlorophyll.

Inverse square law for light intensity (Higher Tier)

$\text{light intensity} \propto \frac{1}{\text{distance}^2}$; doubling the distance from the lamp reduces the light intensity to one-quarter ($\frac{1}{4}$).

Economic control of limiting factors in greenhouses (Higher Tier)

Commercial growers artificially add heat, light, and carbon dioxide to maximize crop photosynthesis rates while balancing input costs to secure maximum profit.

Investigating light intensity on pondweed photosynthesis (Required Practical 5)

Place pondweed in sodium hydrogen carbonate solution, position a lamp at measured distances, allow acclimatisation, count oxygen bubbles per minute, and replicate at varied distances.

Five uses of glucose synthesized by plants

Used in cellular respiration, converted to insoluble starch for storage, used to produce cellulose for cell walls, used to produce lipids for storage, and combined with nitrates to form amino acids.

Definition and metabolic nature of cellular respiration

An exothermic reaction occurring continuously in living cells to transfer the energy required for all living processes.

Equations for aerobic versus muscle anaerobic respiration

Aerobic: $C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6CO<em>2 + 6H</em>2O$; Muscle anaerobic: $\text{glucose} \rightarrow \text{lactic acid}$ (transfers much less energy due to incomplete glucose oxidation).

Equation and commercial importance of yeast fermentation

$\text{glucose} \rightarrow \text{ethanol} + \text{carbon dioxide}$; utilized commercially in brewing beer and wine (alcohol production) and bread making ($CO_2$ dough rising).

Cardiorespiratory adjustments during physical exercise

Heart rate, breathing rate, and breath volume increase to supply exercising muscles with more oxygenated blood for cellular respiration.

Definition and clearance of oxygen debt (Higher Tier)

The extra oxygen required after exercise to react with accumulated lactic acid transported from muscles to the liver, converting it back into glucose.

Definition of metabolism and three examples

The sum of all reactions in a cell or the body; includes converting glucose to starch/cellulose/glycogen, synthesizing lipids from glycerol and fatty acids, and breaking down proteins into urea.

Definition and biological significance of homeostasis

The regulation of internal cellular and organism conditions to maintain optimal environments for enzyme action and all cell functions.

Three internal conditions controlled by human homeostasis

Blood glucose concentration, core body temperature, and water levels.

Three essential components of all biological control systems

Receptors (detect environmental stimuli), coordination centres (brain, spinal cord, pancreas to process information), and effectors (muscles or glands to restore optimum levels).

Sequence of structures in a human nervous pathway

$$\text{stimulus} \rightarrow \text{receptor} \rightarrow \text{sensory neurone} \rightarrow \text{CNS coordinator} \rightarrow \text{motor neurone} \rightarrow \text{effector} \rightarrow \text{response}$$

Mechanism and purpose of a reflex arc

A rapid, involuntary pathway bypassing the conscious brain to protect tissues from harm, using chemical neurotransmitters across synapses between sensory, relay, and motor neurones.

Method for investigating reaction time (Required Practical 6)

Drop a vertical metre ruler between a subject's thumb and index finger without warning, record the catch centimetre mark, convert to reaction time, and assess variables like caffeine.

Principles of the human endocrine system

Endocrine glands secrete hormones directly into the bloodstream to target organs; responses are slower and longer-lasting than rapid nervous electrical impulses.

Role of the pituitary gland as the 'master gland'

Secretes several hormones into the blood in response to body conditions, stimulating other endocrine glands to secrete hormones to produce specific effects.