Biology O Level Conceptual Learning Notes – Units 1 to 8 (Flashcards)

A comprehensive set of quiz-style questions and answers covering cell structure, diffusion/ osmosis, transport, nutrition, digestion, enzymes, respiration, excretion, circulatory system, and related topics from Units 1–8.

What is a cell?

A basic unit of life; all animals and plants are made of cells. It contains living material called protoplasm, comprising the cell membrane, cytoplasm, and nucleus.

What is protoplasm?

The living material of the cell, made up of cell membrane, cytoplasm, and nucleus.

Which plant cell structures are absent in animal cells that are present in plant cells?

Cell wall and chloroplasts; plants also typically have a large central vacuole.

What is the function of the cell membrane?

It surrounds the cell, is partially permeable, and controls movement of substances in and out.

What is the function of the cell wall?

Protects the plant cell from injury and gives it a fixed shape; made of cellulose; fully permeable.

What are organelles?

Cellular structures that perform specific functions within the cell.

What is the nucleus and its functions?

An organelle surrounded by the nuclear membrane; controls cell activities and contains chromosomes (DNA).

What are chromosomes?

Long thread-like structures made of proteins and DNA that carry hereditary information.

What is the Golgi body?

A series of flattened sacs that chemically modify substances from the ER and package them into vesicles for secretion.

What is the endoplasmic reticulum (ER)? Distinguish between rough and smooth ER.

RER has ribosomes and transports proteins; SER lacks ribosomes and synthesises lipids and detoxifies substances.

What is the vacuole and how does it differ between plant and animal cells?

A membrane-bound storage organelle. Plant cells have a large central vacuole; animal cells have small, numerous, temporary vacuoles.

What is the mitochondrion known as and what is its role?

The powerhouse of the cell; site of aerobic respiration that releases energy from glucose.

What is chloroplast and where is it found?

Organelle containing chlorophyll that traps light for photosynthesis; found in plant cells and some algae.

What is ribosome function and where are they located?

Sites of protein synthesis; can be attached to rough ER or free in cytoplasm.

What is a diffusion gradient?

Difference in concentration between two regions; diffusion occurs from high to low concentration.

What is diffusion and is it energy-dependent?

Movement of particles down a concentration gradient; it is a passive (energy-free) process.

Name three factors that affect the rate of diffusion.

Surface area-to-volume ratio, temperature, and diffusion distance.

How does SA:V ratio affect diffusion rate?

A larger surface area relative to volume increases the rate of diffusion across the cell membrane.

What is diffusion distance and how does it influence diffusion rate?

The distance particles must move; shorter distance increases diffusion rate.

What is osmosis?

Movement of water molecules from higher water potential to lower water potential across a partially permeable membrane; passive.

What is water potential?

The measure of the tendency of water to move; dilute solutions have higher water potential.

What is plasmolysis and when does it occur?

Cells shrink and cytoplasm pulls away from the cell wall in a concentrated (hypertonic) solution (plants).

What happens to animal red blood cells in a hypertonic solution?

Crenation — they shrink as water leaves the cell.

What happens to plant cells in a hypotonic solution?

Turgor pressure increases; cells become turgid due to water intake.

What is diffusion distance in biological contexts?

The distance between two regions of different concentrations; shorter distance increases diffusion rate.

What is active transport?

Movement of substances across a cell membrane against a concentration gradient, requiring energy from respiration.

Give two examples of active transport in humans and plants.

Glucose uptake by intestinal cells; mineral ion uptake by root hair cells.

What are carbohydrates?

Organic molecules composed of carbon, hydrogen, and oxygen in a 2:1 H:O ratio; include sugars and starches.

What are the three types of carbohydrates?

Monosaccharides (single sugars), disaccharides (double sugars), and polysaccharides (complex carbohydrates).

What are monosaccharides? Give examples.

Simple sugars such as glucose and fructose; basic units of carbohydrates.

What are disaccharides? Give examples.

Two monosaccharides joined; examples include maltose (glucose + glucose) and sucrose (glucose + fructose).

What are polysaccharides? Name three examples and their roles.

Starch, cellulose, and glycogen; starch and glycogen store energy; cellulose forms plant cell walls and provides fibre.

What is the digestion process of starch in the mouth?

Salivary amylase converts starch to maltose (maltose is digested further by maltase).

What is the function of fats and their main components?

Fats supply energy, insulation, and act as a solvent; they are composed of glycerol and fatty acids.

Describe the digestion of fats.

Fats are broken down by lipases into glycerol and fatty acids.

What is the test for fats?

Ethanol emulsion test: shake fats with ethanol and water to form a white emulsion.

What are proteins made of?

Proteins are made of amino acids linked by peptide bonds to form polypeptides and proteins.

What is the Biuret test?

Blue Biuret solution turns violet in the presence of proteins.

What are enzymes?

Biological catalysts, usually proteins, that speed up reactions without being consumed. They are protein-folded into active sites and show specificity.

What is the lock-and-key model?

A theory that describes enzyme specificity: only substrates with a shape complementary to the active site bind.

What is activation energy and how do enzymes affect it?

Activation energy is the energy needed to start a reaction; enzymes provide a lower-energy pathway, speeding up the reaction.

What are the two types of enzyme-catalyzed reactions discussed?

Catabolic reactions break down large molecules; anabolic reactions build up complex molecules.

What are optimal temperature and pH in enzyme activity?

Enzymes have an optimum temperature and pH; deviations reduce activity or denature the enzyme.

What are the major components of the human digestive system?

Mouth, pharynx, esophagus, stomach, small intestine, large intestine, plus liver, gall bladder, pancreas.

What is peristalsis?

Rhythmic waves of muscle contractions moving food along the gut.

What enzymes are secreted by the pancreas and what do they do?

Pancreatic amylase (starch to maltose), protease (proteins to peptides), lipase (fats to fatty acids and glycerol).

What is emulsification and which organ is responsible?

Breaking down fats into smaller droplets to increase surface area; bile salts in the liver/gall bladder perform this in the small intestine.

Where does most absorption occur in the digestive system and what structures aid it?

In the ileum of the small intestine; villi and microvilli increase surface area for absorption into blood capillaries and lacteals.

What is the hepatic portal vein and its role?

A vessel that carries absorbed sugars and amino acids from the small intestine to the liver for processing.

What are the main functions of the liver?

Regulate blood glucose (store glycogen; release glucose via glycogenolysis), detoxify substances, produce bile.

What is deamination?

Removal of amino groups from amino acids in the liver to form urea for excretion; remaining carbon skeletons can be converted to glucose or glycogen.

What is osmoregulation?

Control of water potential and solute concentration in the blood to maintain stable internal conditions.

What hormone regulates water reabsorption in the kidney?

Antidiuretic hormone (ADH), released by the pituitary; increases collecting duct permeability to water when needed.

What is dialysis and why is it used?

A process that acts as an artificial kidney, removing waste products from the blood when kidneys fail.

What is ultrafiltration in the kidney?

Filtration of plasma through the glomerulus into Bowman's capsule due to high blood pressure, forming glomerular filtrate.

What is glomerular filtrate and what does it contain?

Fluid filtered from blood in the glomerulus; contains water, glucose, amino acids, minerals, and urea, but not proteins or cells.

Where do glucose and amino acids get reabsorbed in the nephron?

In the proximal convoluted tubule, via active transport (glucose and amino acids) and diffusion/active transport for salts.

Why is urea not reabsorbed along the nephron?

Urea remains in the filtrate to be excreted in urine; it is a waste product.

What is the function of the nephron’s Loop of Henle?

Reabsorbs water and minerals; contributes to water balance and urine concentration.

What is the distinction between egestion and excretion?

Egestion is the removal of undigested food from the digestive system; excretion removes metabolic wastes from body.

What are the main components of blood plasma and its functions?

Plasma is mostly water and carries soluble proteins, minerals, nutrients, hormones, excretory products, and helps transport cells.

What are the ABO blood groups based on?

Antigens (A and B) on red blood cells and antibodies in plasma; determines compatibility for transfusions.

What is agglutination in blood transfusions?

Clumping of red blood cells when antibodies bind to antigens, potentially blocking vessels.

What is tissue rejection in transplants and how can it be prevented?

Recipient immune system may attack donor tissue; prevention includes tissue matching and immune-suppressing drugs.

What are the main functions of platelets?

Fragments of cytoplasm that help form clots to prevent excessive bleeding.

What is the cardiac cycle?

Sequence of atrial and ventricular systole and diastole producing a heartbeat; includes valve actions and heart sounds.

Which parts of the heart have thicker walls and why?

Ventricles have thicker walls than atria to generate higher pressure; left ventricle is thicker than right to supply the rest of the body.

What causes the ‘lub’ and ‘dub’ sounds in the heartbeat?

Lub: atrioventricular valves (bicuspid/tricuspid) close during ventricular systole; Dub: semilunar valves close during diastole.

What causes coronary heart disease and what are risk factors?

Atherosclerosis and blood clots in coronary arteries; risk factors include unhealthy diet, age, smoking, genetics, sedentary lifestyle.

What is the primary site of gas exchange in the lungs?

Alveoli with a thin epithelium and a dense capillary network that interface with air in the alveolar space.

What is the role of haemoglobin in oxygen transport?

Haemoglobin binds oxygen in the lungs to form oxyhaemoglobin and releases it in tissues with low oxygen.

What is the mechanism of breathing in humans?

Diaphragm contracts and flattens; external intercostal muscles contract; volume increases and air is drawn in.

What are the components and harmful components of cigarette smoke and their effects?

Nicotine increases heart rate and blood pressure; carbon monoxide reduces oxygen transport by binding haemoglobin; tar is carcinogenic and damages lungs.

What are the main parts of the respiratory system?

Nose, pharynx, larynx, trachea, bronchi, bronchioles, alveoli, and associated capillaries; supported by ribs and diaphragm.

What is the function of cilia and mucus in the trachea?

Gland cells secrete mucus to trap particles; cilia sweep mucus upwards to the throat.

What is the purpose of the rib cage and diaphragm in breathing?

Ribs and intercostal muscles plus diaphragm enable changes in thoracic volume to breathe in and out.