Edexcel GCSE Biology - Topic 1

Acrosome

organelle in sperm tip containing enzymes digest egg cell membrane. streamlined shape aids swimming

Active Site

specific region on enzyme where substrate binds, reaction occurs

Active Transport

movement of substances from a low to higher concentration (against concentration gradient) across membrane, using ATP from respiration

Benedict's Test

chemical test for reducing sugars using benedict’s solution and heat, producing reddish-brown colour when reducing sugars present

Carbohydrases

enzymes break down carbohydrates to simple sugars

Carbohydrate

large molecule synthesised from simple sugars

Cell

basic building block of all living organisms

Cell Membrane

partially permeable barrier surrounding cell, controls what enters and leave cell

Cell Wall

cellulose-based outer layer strengthens plant cells, also present in algal cells

Chromosome

long, coiled DNA molecule carrying genetic information, genes

Cilia

hair-like structures on ciliated epithelial cells, waft substances across tissue surface in one direction

Ciliated Epithelial Cell

type of epithelial cell lining surface(s) of respiratory tract and uterus. specialised to waft bacteria trapped by mucus to the stomach

Concentration Gradient

difference in concentration between two areas

Denaturation

exposure to high temperatures or extreme pH, permanent change in shape of enzyme's active site prevents substrate binding

Diffusion

net spreading of particles from a high to lower concentration (down concentration gradient)

Diploid Cell

cell containing 2 copies of each chromosome (i.e. a full set of chromosomes)

Egg Cell

specialised female sex cell involved in reproduction

Electron Microscope

type of microscope using magnet-focused beam of electrons to produce image of specimen. greater magnification, resolution than light microscope

Enzyme

biological catalyst increases rate of reactions in living organisms without being used up

Eukaryotic Cell

type of cell in plants and animals containing a nucleus

Haploid Cell

cell containing single copy of each chromosome (i.e. half the number of chromosomes).

Iodine Test

chemical test for starch using iodine solution. positive result = blue-black colour

Light Microscope

instrument with two lenses, magnify visible light reflecting off specimen, usually illuminated from underneath. lower magnification, resolution than electron microscope

Lipases

enzymes break down lipids to fatty acids, glycerol

Lipid

large molecule synthesised from fatty acids and glycerol

Lock and Key Hypothesis

theory describing how substrates must be correct shape to bind to enzyme’s active site

Magnification

ratio of measured to actual size
magnification = image size ÷ real size

Micrometre (µm)

quantitative unit of length = ×10​-6​ metre.

millimetre (mm)

quantitative unit of length = ×10​-3​ metre

Nanometre (nm)

quantitative unit of length = ×10​-9​ metre

Nucleus

organelle found in most eukaryotic cells, contains DNA coding for particular protein needed for new cells, controls cell’s activities, enclosed in nuclear membrane

Organelle

specialised structure found inside cell

Osmosis

diffusion of water molecules from region of high to lower water concentration, across partially permeable membrane

Picometre (pm)

quantitative unit of length = ×10​-12​ metre

Prokaryotic Cell

type of cell found in bacteria, no nucleus

Proteases

enzymes break down proteins into amino acids

Protein

large molecule synthesised from amino acids

Rate of reaction

speed at which reactants converted into products = Change ÷ Time

Resolution

smallest distance between two distinguishable objects

Specialised cell

cell with structure adapted to its function

Specificity

ability of an enzyme to catalyse particular reaction(s), specific substrate fits enzyme’s active site

Sperm Cell

specialised male sex cell carry male's DNA to egg cell (ovum) for successful reproduction

Cytoplasm

liquid substance containing enzymes, organelles, where chemical reactions occur

Mitochondria

organelle, site of aerobic respiration, providing ATP for cell

Ribosomes

site of protein protein synthesis, found on rough endoplasmic reticulum

Chloroplasts

site of photosynthesis, provide food for plant, contains green chlorophyll pigment

Permanent Vacuole

in plant cell cytoplasm, contains cell sap, improves cell rigidity

Chromosomal DNA

circular DNA floating in cytoplasm of bacterial cells which have no nucleus

Plasmid

small loops of DNA found in prokaryotic cell cytoplasm, coding for extra genes to those coded for in chromosomal DNA

Flagella

long thin whiplike tails attached to bacteria allow movement

Differentiation

process cell gains new sub-cellular structures suited to its role

Stem Cells

cells retain ability to differentiate throughout whole life

Aerobic Respiration

reactions in mitochondria providing energy for cell
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
glucose + oxygen → carbon dioxide + water + energy

Photosynthesis

process in chloroplasts providing food for plant
6H₂O + 6CO₂ → 6O₂ + C₆H₁₂O₆

Cell Sap

liquid in permanent vacuole helps improve cell rigidity

Peptidoglycan

compound makes up cell wall bacterial cells

Cellulose

substance makes up plant cell walls

Long Tail

feature of sperm cells aids in swimming

Haploid Nucleus

nucleus with 23 chromosomes, opposed to 46 found in most other body cells

Fertilisation

process egg cell accepts one sperm cell becomes impermeable

Root Hair Cells

specialised take up water by osmosis and mineral ions by active transport from soil.
large surface area (more water), large permanent vacuole (speed of water movement), mitochondria (energy)

Large Surface Area

feature of root hair cells allows more water to move in

Xylem Cells

specialised transport water + mineral ions from roots to shoots, up plant

Lignin

chemical deposited in xylem cells causes them to die, become hollow

Phloem Cells

specialised carry products of photosynthesis (food) to all parts plants

Sieve Plates

structures formed by the phloem cell walls allow movement of substances

Maximum Magnification of Light Microscope

approximately 2000x.

Resolving Power of Light Microscope

200nm, affecting the ability to distinguish between two points (resolution)

Scanning Electron Microscope

type of electron microscope creates 3D images at slightly lower magnification

Transmission Electron Microscope

type of electron microscope creates 2D images detailing organelles. used to discover viruses, poliovirus, smallpox, ebola

Maximum Magnification of Electron Microscope

up to 2,000,000x.

Resolving Power of Transmission Electron Microscope

0.2nm.

Uses of Transmission Electron Microscopes

discover viruses such as poliovirus, smallpox, and Ebola, still used today

Uses of Electron Microscopes

examine proteins in much greater detail than possible with a light microscope

Magnification of Light Microscope

magnification of the eyepiece lens x magnification of the objective lens

Object Size

size of image/magnification = size of object.

Standard Form

expressing very large or small numbers by multiplying a certain number by a power of 10.
e.g. x10-n

Orders of Magnitude

understand how much bigger or smaller one object is than another

Centi Prefix

multiply unit by 0.01.

Milli prefix

multiply unit by 0.001.

Micro prefix

multiply unit by 0.000001.

Nano prefix

multiply unit by 0.000000001.

Estimations

useful when specimen quantity unknown or if counting is time-consuming

Eyepiece

part we look through to view specimens

Barrel of a Light microscope

upper part - moved up, down to focus image

Turret of a Light Microscope

part rotated to change the magnification lens

Lens of a Light Microscope

increases magnification of specimen

Stage of a Light Microscope

flat surface on which we place the specimen.

Steps to use a Light Microscope

slide on stage + look through eyepiece
turn focus wheel for clear image
start with lowest objective lens magnification
increase magnification and refocus

Chemical Stains

substances used to make parts of specimen more visible under microscope (contrast, specificity)

Iodine (stain)

blue-black colour when starch present

Methylene Blue (stain)

stains animal nucleus blue

Toluidine Blue (stain)

stains DNA and RNA blue

Phloroglucinol

stains lignin in plant cell walls red-pink

Coverslip

thin piece of glass placed over specimen on slide avoid air bubbles

Actual Size

= measured size ÷ magnification

Enzyme-Substrate Complex

intermediate formed when substrate binds to enzyme

Optimum pH

pH level at which an enzyme functions best, around 7 for most

Optimum Temperature

temperature range at which enzyme operates most efficiently, around 37^oC in humans.

Saturation Point

substrate concentration at which rate of reaction doesn’t increase, despite additional substrate