IGCSE Biology Coursebook - Chapters 2 to 6 Vocabulary

A comprehensive set of vocabulary flashcards covering basic cell biology, biological molecules, movement across membranes, enzymes, and plant nutrition as presented in the Cambridge IGCSE Biology Coursebook.

cells

The smallest units from which all organisms are made.

multicellular

Organisms that contain millions of cells.

unicellular

Organisms that are made of just a single cell, such as bacteria and yeast.

light microscope

A type of microscope used in school laboratories that shines light through a specimen and uses glass lenses to magnify the image.

electron micrograph

An image made using an electron microscope, which uses a beam of electrons instead of light to see smaller structures inside a cell.

cell membrane

A very thin layer surrounding the cytoplasm of every cell that controls what enters and leaves the cell.

partially permeable

A property of a membrane that allows some molecules and ions to pass through, but not others.

cell wall

A tough, fully permeable layer outside the cell membrane found in plants, fungi and bacteria; in plants, it is made mainly of cellulose.

cytoplasm

The jelly-like material that fills a cell and contains many substances dissolved in it, where many metabolic reactions take place.

metabolic reactions

The chemical reactions of life that take place in living organisms.

vacuole

A fluid-filled space inside a cell, separated from the cytoplasm by a membrane.

cell sap

The fluid, consisting of a solution of sugars and other substances, that fills the large vacuoles in plant cells.

vesicle

A very small vacuole found in animal cells.

nucleus

A structure containing DNA in the form of chromosomes, where genetic information is stored.

chromosome

A length of DNA found in the nucleus of a cell; it contains genetic information in the form of many different genes.

DNA

A molecule that contains genetic information, in the form of genes, that controls the proteins that are made in the cell.

chloroplasts

Small structures inside some plant cells, containing chlorophyll, where photosynthesis takes place.

chlorophyll

A green pigment found in chloroplasts that absorbs energy from sunlight for photosynthesis.

starch grains

Tiny pieces of starch stored in some plant cells that have been made by photosynthesis.

mitochondrion

A small structure in a cell where aerobic respiration occurs to release energy from glucose.

aerobic respiration

Chemical reactions in mitochondria that use oxygen to break down glucose and other nutrient molecules to release energy.

ribosomes

Very small structures in a cell that use information on DNA to make protein molecules.

bacteria

Unicellular organisms whose cells do not contain a nucleus.

prokaryotic cells

Cells with no nucleus; bacteria are an example of this cell type.

plasmids

Small, circular molecules of DNA found in many prokaryotic cells in addition to the main bacterial chromosome.

tissue

A group of similar cells that work together to perform a particular function.

organ

A group of different tissues that work together to perform a particular function.

organ system

Several organs that work together to perform a particular function, such as the digestive system.

magnification

How many times larger an image is than the actual object, calculated as $\text{magnification} = \frac{\text{size of image}}{\text{size of actual object}}$.

micrometre ($\mu m$)

A unit of measurement used for very small objects where $1\,\mu m = 1 \times 10^{-6}\,m$ and there are $1000\,\mu m$ in $1\,mm$.

diffusion

The net movement of particles from a region of their higher concentration to a region of their lower concentration (down a concentration gradient) as a result of their random movement.

kinetic energy

The energy of moving objects; particles have more of this at higher temperatures.

net movement

The overall or average movement of particles.

concentration gradient

An imaginary 'slope' from an area of high concentration to an area of low concentration.

solute

A substance that has dissolved in a liquid.

solvent

The liquid in which a solute dissolves; in organisms, this is always water.

independent variable

The variable that is changed in an experiment.

dependent variable

The variable that is measured during an experiment to collect results.

osmosis

The diffusion of water molecules through a partially permeable membrane.

water potential

A measure of the quantity of water; a dilute solution has high water potential, while a concentrated solution has low water potential.

turgid

A description of a plant cell that is tight and firm due to water pushing outwards on the cell wall.

turgor pressure

The pressure of water pushing outwards on a plant cell wall.

flaccid

A description of a plant cell that is soft and floppy due to loss of water.

plasmolysed

A description of a cell in which the cell membrane tears away from the cell wall due to extreme water loss.

active transport

The movement of molecules or ions through a cell membrane from a region of lower concentration to a region of higher concentration (against a concentration gradient) using energy from respiration.

carrier proteins

Protein molecules in cell membranes that use energy to change shape and move ions or molecules into or out of a cell.

carbohydrates

Substances including sugars, starch, and cellulose that contain the elements carbon, hydrogen, and oxygen.

glucose

A simple sugar with the formula $C_6H_{12}O_6$ used in respiration to release energy.

glycogen

A carbohydrate used as an energy store in animal cells.

starch

A carbohydrate used as an energy store in plant cells.

iodine solution

A solution used to detect starch; it turns from orange-brown to blue-black when starch is present.

Benedict's solution

A blue liquid used to test for reducing sugars; it turns orange-red when heated with them.

reducing sugars

Sugars such as glucose that turn Benedict's solution orange-red when heated.

lipids

Fats and oils containing carbon, hydrogen, and oxygen that are insoluble in water and used as energy stores.

emulsion

A liquid containing two substances that do not fully mix, such as the milky appearance formed in the ethanol emulsion test for fats.

proteins

Substances molecules made of many amino acids linked together; they contain carbon, hydrogen, oxygen, nitrogen and sometimes sulfur.

amino acids

The 20 different kinds of smaller molecules that link together in long chains to form proteins.

antibodies

Protein molecules secreted by white blood cells that bind to pathogens to help destroy them.

biuret reagent

A blue solution that turns purple or violet when mixed with proteins.

DCPIP

A purple liquid used to test for vitamin C, which becomes colourless in its presence.

nucleotides

Molecules that link together into long chains to make up a DNA molecule.

base

A component of DNA (A, C, G, or T) whose sequence determines the proteins made in a cell.

complementary base pairing

The specific way DNA bases pair up where A always pairs with T and C always pairs with G.

catalyst

A substance that increases the rate of a chemical reaction and is not changed by the reaction.

enzymes

Proteins that function as biological catalysts in all metabolic reactions.

amylase

An enzyme that catalyses the breakdown of starch to maltose.

protease

An enzyme that catalyses the breakdown of protein to amino acids.

catalase

An enzyme that catalyses the breakdown of hydrogen peroxide to water and oxygen.

substrate

The substance that an enzyme causes to react.

active site

The part of an enzyme molecule with a specific shape to which the substrate temporarily binds.

product

The new substance formed by a chemical reaction.

enzyme-substrate complex

The short-lived structure formed as the substrate binds temporarily to the active site of an enzyme.

optimum

The 'best' conditions, such as temperature or pH, at which an enzyme's activity is at its greatest.

denature

The process where an enzyme loses its shape due to high temperature or extreme pH, making it unable to catalyse reactions.

photosynthesis

The process by which plants synthesise carbohydrates from raw materials ($CO_2$ and $H_2O$) using energy from light.

sucrose

A sugar made of glucose and fructose linked together, which is the form in which carbohydrates are transported in plants.

vascular bundles

Collections of xylem tubes and phloem vessels that form the veins in a leaf.

cuticle

A thin layer of wax that covers the upper surface of a leaf to reduce water loss.

palisade mesophyll

The layer of tall, narrow cells beneath the upper epidermis where most photosynthesis happens.

spongy mesophyll

The layer of rounded cells beneath the palisade mesophyll that contains many air spaces for gas diffusion.

stomata

Openings in the surface of a leaf, mostly on the lower surface, that allow gas exchange.

guard cells

A pair of cells surrounding a stoma that control its opening and closing.

destarching

Leaving a plant in the dark for long enough for it to use up its starch stores before an experiment.

control

A standard sample used for comparison to find the effect of changing a variable.

limiting factor

A factor in short supply (such as light intensity, $CO_2$ concentration, or temperature) that stops photosynthesis from happening at a faster rate.