Key Concepts in Biology: MRS GREN and More

MRS GREN

Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.

Movement

The ability of an organism to change position or move parts of its body.

Respiration

The chemical process of releasing energy from glucose (usually using oxygen).

Sensitivity

The ability to detect and respond to changes in the environment (stimuli).

Growth

An increase in size and mass using materials from food.

Reproduction

The process of producing new individuals or offspring (asexual or sexual).

Excretion

The removal of toxic waste substances made in cells (e.g. urea, CO₂).

Nutrition

Taking in food or nutrients for energy, growth, and repair.

Biology

The study of life — from cells to whole ecosystems.

Excretion (repeated)

Removal of metabolic waste (like urea or CO₂).

Difference between excretion and egestion

Excretion removes waste made by cells; egestion removes undigested food.

Eukaryotic cell

A cell with a nucleus and membrane-bound organelles.

Prokaryotic cell

A cell without a nucleus; e.g. bacteria.

Eukaryotic kingdoms

Animalia, Plantae, Fungi, Protista.

Prokaryotic kingdoms

Bacteria and Archaea.

Size of eukaryotic vs prokaryotic cells

Eukaryotic ~50μm, Prokaryotic ~1μm.

Magnification formula

Image size ÷ Actual size.

Asexual reproduction

One parent produces genetically identical offspring.

Bacteria reproduction

By binary fission — a type of asexual reproduction.

Yeast reproduction

By budding — a form of asexual reproduction.

Sexual reproduction

Two parents produce genetically varied offspring.

Zygote

A fertilised egg formed when sperm and egg fuse.

Cell specialisation

When cells develop specific roles (e.g. nerve cells).

Stem cell

An undifferentiated cell that can become specialised.

Differentiation

The process of becoming specialised.

Tissue

A group of similar cells doing the same job.

Organ

A structure made of tissues with a specific function.

Organ system

A group of organs working together.

Organism

A living thing made of organ systems.

Autotroph

An organism that makes its own food (e.g. plants).

Heterotroph

An organism that consumes others for food (e.g. animals).

Balanced equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

Photosynthesis location

In chloroplasts using chlorophyll.

Light colours that increase photosynthesis

Red and blue (green is reflected).

Greenhouse effect on photosynthesis

More light, warmth and CO₂ increases glucose production.

Uses of glucose in plants

Making starch, cellulose, energy (respiration), proteins and lipids.

Mineral absorption in plants

Through roots — potassium, phosphate, magnesium, etc.

Word equation for aerobic respiration

Glucose + Oxygen → Carbon dioxide + Water.

Aerobic respiration location

In the mitochondria.

Anaerobic respiration (animals)

Glucose → Lactic acid.

Anaerobic respiration (yeast)

Glucose → Alcohol + Carbon dioxide.

Aerobic vs anaerobic respiration

Aerobic releases more energy (ATP).

Digestive system function

Breaks down food and absorbs nutrients.

Mouth function

Starts digestion by chewing and mixing food with saliva.

Stomach function

Uses acid and enzymes to break food down.

Small intestine function

Absorbs nutrients into the blood.

Liver function

Produces bile to help digest fats.

Gallbladder function

Stores bile and releases it into the intestine.

Pancreas function

Makes enzymes: amylase, protease, lipase.

Large intestine function

Absorbs water and forms faeces.

Enzyme

A biological catalyst that speeds up reactions.

Catalyst

A substance that speeds up a reaction without being used.

Biological catalyst

A biological catalyst that speeds up reactions.

Active site

The part of the enzyme that binds to the substrate.

Amylase

An enzyme that breaks down carbohydrates into simple sugars.

Protease

An enzyme that breaks down proteins into amino acids (e.g. pepsin).

Lipase

An enzyme that breaks down lipids into fatty acids and glycerol.

Nuclease

An enzyme that breaks down nucleic acids into nucleotides.

Test for starch

Iodine → turns blue-black if present.

Test for glucose

Benedict's + heat → red/orange if present.

Test for protein

Biuret test → purple if present.

Test for lipids

Ethanol test → cloudy white emulsion if present.

Stamen

The male parts of a flower, consisting of anther + filament.

Carpel

The female parts of a flower, consisting of stigma + style + ovary.

Anther

Produces pollen (male gametes).

Stigma

Collects pollen.

Ovary in flowers

Contains ovules (egg cells).

Pollination

Transfer of pollen from anther to stigma.

Fertilisation in plants

Happens in the ovary, when pollen fuses with an ovule.

Function of the testes

Produce sperm and testosterone; site of meiosis.

Function of the scrotum

Protects testes and controls temperature.

Function of the urethra (male)

Transports urine and semen out of the body.

Epididymis

Stores, matures, and moves sperm.

Prostate gland

Adds fluid to form semen.

Seminal vesicle

Adds nutrient-rich fluid to semen.

Ejaculatory duct

Delivers sperm into the urethra during ejaculation.

Vas deferens

Transports sperm from testes to urethra.

Penis

Transfers semen into the vagina.

Sperm duct

Connects testes to urethra through the prostate.

Cervix

Narrow opening between uterus and vagina; allows fluid flow.

Vagina

Birth canal; receives sperm during intercourse.

Uterus

Where a fertilised egg implants and baby develops.

Ovaries

Produce eggs and hormones (oestrogen and progesterone).

Oviducts

Transport eggs to the uterus; site of fertilisation.

Fundus

Top of uterus; supports pregnancy and hormone control.

Endometrium

The uterus lining that thickens and sheds monthly.

Ovulation

Release of an egg from the ovary (around day 14).

Menstrual cycle

~28-day cycle preparing uterus for pregnancy.

Oestrogen

Builds the uterus lining during the cycle.

Progesterone

Maintains the uterus lining after ovulation.

Implantation

When a fertilised egg embeds into the uterine wall.

Gestation

Time between fertilisation and birth (~9 months).

Placenta

Transfers oxygen/nutrients to the fetus; removes waste.

Puberty

The time when the body develops to become reproductive.

Hormone causing puberty in boys

Testosterone.

Hormone causing puberty in girls

Oestrogen.

Changes during puberty in boys

Voice deepens, facial hair, sperm production, muscle growth.

Changes during puberty in girls

Breasts grow, hips widen, periods start, body hair.

Seminal fluid

Fluid that nourishes and helps sperm move.

Semen

A mixture of sperm cells and seminal fluid.