Biology P1 GCSE

Prokaryotic cells

Bacteria cells (much smaller than Euk)

-Cell wall

-Cell membrane

-Cytoplasm

-Singular strands of DNA and plasmids (found in cytoplasm)

Eukaryotic cells

Animal and Plant Cells

-Cell Membrane

-Cytoplasm

-Nucleus (containing DNA)

Organelles

structures in a cell that have different functions

Units of measurement

Multiplying Factor	Name (symbol)	Scientific Notation
0.01	centi (c)	10-2
0.001	milli (m)	10-3
0.000 001	micro (µ)	10-6
0.000 000 001	nano (n)	10-9

Nucleus - plant, animal

-Contains DNA coding for a particular protein needed to build new cells.

- Enclosed in a nuclear membrane.

Cytoplasm - plant, animal, bacteria

-Liquid substance in which chemical reactions occur.

-Contains enzymes (biological catalysts, i.e. proteins that speed up

the rate of reaction).

-Organelles are found in it

Cell Membrane - plant, animal, bacteria

Controls what enters and leaves the cell

Mitochondria - plant, animal

Where aerobic respiration reactions occur, providing energy for the cell

Ribosomes - plant, animal

- Where protein synthesis occurs.

- Found on a structure called the rough endoplasmic reticulum

Chloroplasts - plant

-Where photosynthesis takes place, providing food for the plant

-Contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis.

Permanent Vacuole - plant

-Contains cell sap

-Found within the cytoplasm

-Improves cell’s rigidity

Cell wall - plant, algal

-Made from cellulose

-Provides strength to the cell

Cell wall - bacteria

-Made of a different compound

(peptidogylcan)

Singular circular strand of DNA - bacteria

-As they have no nucleus, this floats in the cytoplasm

Plasmids - bacteria

small rings of DNA

What is cell specialisation?

Where cells gain new sub-cellular structures in order to be suited to their role.

Cells can either differentiate once early on or have the ability to differentiate their whole life (these are called stem cells)

How are sperm cells specialised to to carry the male’s DNA to the egg cell (ovum) for successful reproduction

Animals

-Streamlined head and long tail to aid swimming

-Many mitochondria (where respiration happens) which supply the energy to allow the cell to move

-The acrosome (top of the head) has digestive enzymes which break down the outer layers of membrane of the egg cell

How are nerve cells specialised to transmit electrical signals quickly from one place in the body to another

Animals

-The axon is long, enabling the impulses to be carried along long distances

-Having lots of extensions from the cell body (called dendrites) means branched connections can form with other nerve cells

-The nerve endings have many mitochondria which supply the energy to make special transmitter chemicals called neurotransmitters. These allow the impulse to be passed from one cell to another.

How are muscle cells specialised to contract quickly to move bones (striated muscle) or simply to squeeze (smooth muscle, e.g found in blood vessels so blood pressure can be varied), therefore causing movement

animals

-Special proteins (myosin and actin) slide over each other, causing the muscle to contract

-Lots of mitochondria to provide energy from respiration for contraction

-They can store a chemical called glycogen that is used in respiration by mitochondria

How are root hair cells specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots

Plants

-Have a large surface area due to root hairs, meaning more water can move in

-The large permanent vacuole affects the speed of movement of water from the soil to the cell

-Mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell

How are Xylem cells specialised to transport water and mineral ions up the plant from the roots to the shoots

Plants

-Upon formation, a chemical called lignin is deposited which causes the cells to die. They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through

-Lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water

How are Phloem cells: specialised to carry the products of photosynthesis (food) to all parts of the plants

Plants

-Cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell

-Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells.

What is Cell Differentiation in stem cells?

-Stem cells must undergo cell differentiation to become specialised cells

-This means some of their genes are switched on/off to produce different proteins

Cell differentiation in animals

-Happens early in most animal cells (then they lose ability)

-Most specialised cells reproduce through mitosis

-Others (red blood cells) can’t divide so are replaced by adult stem cells

-In mature animals, cell division mostly only happens to repair or replace damaged cells, as they undergo little growth. C

Cell differentiation in plants

-Most plant cells keep ability for life

-Only differentiate when reach final position

Light Microscope

-Robert Hooke, 1665

-2 Lenses: objective and eyepiece

-Illuminated from underneath

-Max. magnification of x2000

-Resolving power of 200nm

-Used to view tissues, cells, large sub-cellular structures

How do the lenses of a Light Microscope work?

The objective lense produces a magnified image, which is then magnified and directed into the eye by the eyepiece lense

Electron microscope

-Used to view deep inside inside sub-cellular structures, such as mitochondria, ribosomes, chloroplasts and plasmids.

-Electrons are used to form an image because they are opposed to light (much smaller wavelength than light waves)

-Magnification of up to 2,000,000, resolving power of 10nm

Types of electron microscope

-Scanning electron microscope: creates 3D images (lower magnification)

-Transmission electron microscope: creates 2D mages detailing organelles

Magnification of a light microscope

magification of eyepiece lens x magnification of objective lens

Size of an object

size of image / magnification

How many pairs of chromosomes in each cell?

23 pairs (each with 1 mother and 1 father)

Sex cells are the exception (half)

The cell cycle stage 1

Interphase: cell grows, organelles grow and increase in number, synthesis of proteins occurs, DNA is replicated (Forms X shape) ,energy stores increased

The cell cycle stage 2

Mitosis: Chromosomes line up at the equator of the cell

Cell fibres pull each chromosome of the ‘X’ to either side of the cell

The cell cycle stage 3

Cytokinesis: Two identical daughter cells form when cytoplasm and cell membranes divide

Why is cell division by mitosis important?

-Growth and development

-Replacing damaged cells

-Asexual reproduction

Types of stem cells

-Embryonic (egg and sperm fuse)

-Adult (form many types of cells)

-Meristems (Root and shoot tips)

Therapeutic Cloning

-Embryo produced with the same genes as patient

-Embryo could be harvested to obtain embryotic stem cells, then grown into cells patient needed (new tissues / organs)

-Advantage: would not be rejected

Benefits of research w/ Stem cells

-Can be used to replace damaged/ diseased body parts

-Unwanted embryos could be used

-Research into process of differentiation

Problems of research w/ Stem cells

-We don’t understand it completely (hard to control)

-Destruction of embryo

-Religious/ Ethical objections

-Stem cells contaminated → individual contaminated

-Money / time consumed

Diffusion

the spreading out of the 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

What do molecules have to be in diffusion?

Small: to be able to move across

Examples of diffusion in the body

Oxygen moves through alveoli into red blood cells, carried to cells across the body → respiration.

CO2 moves from red blood cells → lungs to be exhaled

^ called GAS EXCHANGE

Factors affecting rate of diffusion

-Concentration gradient: greater gradient = faster rate (more particles randomly moving down gradient than against it)
-Temperature greater temp = greater movement (more collisions)

-Surface area of membrane: greater SA = more space for particles, faster diffusion

Why can Single-celled organisms use diffusion to transport molecules into their body from the air?

Relatively large SA to Volume ratio

Why can’t multicellular organisms rely on diffusion alone?

-Small SA to Volume ratio

-Instead they have many adaptations (allow molecules to be transported in and out of cells)

Examples of adaptations to assist diffusion (large SA)

-Lungs: O2 →blood, CO2 →Lungs. Takes place across alveoli, covered in capillaries (supply blood)

-Small intestine: digested food absorbed over membrane of villi

-Gills: gas exchange takes place in fish, gill has gill filaments

Osmosis

the movement of water from a less concentrated solution to a more concentrated one through a partially permeable membrane.

3 features of a good scientific drawing

Scale, Accuracy, Labels

How can scientists study microorganisms?

Microorganisms are very small - scientists need to grow them in a lab using nutrients (culture them)

What does the culture medium contain?

carbohydrates for energy, minerals, proteins and vitamins

Ways to grow microorganisms in the lab?

1. Nutrient broth solution

   2. Agar gel plate

Nutrient broth solution

making a suspension of bacteria to be grown, mixing with sterile nutrient broth (culture medium), stoppering flask with cotton wool (prevent air from contaminating), shaking regularly to provide oxygen for growing bacteria

Agar gel plate

agar acts as culture medium, bacteria grown on it form colonies on the surface

to make the plate: hot jelly poured into petri dish, left to cool and set (all sterilised)

wire loops (inoculating loops) dipped in a solution of microorganism and spread over agar evenly

lid taped on, plate incubated for a few days (microorganisms can grow)

Why is the petri dish and culture media sterilised before use? (usually done by autoclave)

likely to be contaminated (other microorganisms can compete with desired bacteria)

Why is inoculating loop sterilised?

Kills unwanted organisms

Lid of petri dish is sealed because..

stops airborne microorganisms from contaminating culture

should not be sealed all the way (harmful anaerobic bacteria)

Petri dish is stored upside down because…

will prevent condensation from the lid landing on the agar surface & disrupting growth

Why should the culture be incubated at 25 degrees?

if temp was higher (nearer 37 - human body temp), more likely bacteria that could be harmful to humans would be able to grow (optimum temp)

Why does water move from dilute to concentrated?

area of high water potential → low water potential (down concentration gradient)

osmosis is PASSIVE (doesn’t use energy)

Why will water move into our cells?

Cytoplasm contains salts and sugars so when cell is placed in dilute solution, water moves inH

Hypertonic solution

any external solution that has a high solute concentration and low water concentration compared to body fluids

Isotonic soluion

any external solution that has the same solute concentration and water concentration compared to body fluids

Osmosis in animals

-External solution dilute = move into animal cells and they will burst

-External solution concentrated = water leave cell causing it to become shrivelled

Osmosis in plants

-External solution more dilute = water moves into cell and vacuole (swell, turgor)

-External solution less dilute = water moves out of cell, becomes soft. eventually cell membrane moves away from cell wall and it will die

Active transport

movement of particles from area of lower concentration to higher concentration (against concentration gradient)

not passive (requires energy from respiration)

active transport in root hairs

takes up water and mineral ions (healthy growth) from soil

minerals = higher conc in cell (no diffusion)

requires energy from respiration

Active transport in the gut

glucose & amino acids from food move from gut → bloodstream
required to move sugar to the blood against concentration gradient

What is the digestive system made up of?

Glands (salivary glands and the pancreas) = produce digestive juices containing enzymes

Stomach = produces hydrochloric acid to kill bacteria and to provide the optimum pH for the protease enzyme to work.

Small intestine = where soluble molecules are absorbed into the blood.

Liver = produces bile which is stored in the gall bladder, which helps with the digestion of lipids.

Large intestine = absorbs water from undigested food to produce faeces. This passes out of your body through the rectum and anus.

Enzyme

Biological catalyst (increases rate of reaction without being used up)

-present in many reactions (can be controlled)

-breaks up large molecules and joins small ones

-protein molecules (shape vital to function because each enzyme has uniquely shaped active site where substrate binds)

Enzyme optimum pH and temperature

Required because they are protein

-Optimum temp around 37 degrees (body temp)

-Optimum pH for most enzymes is 7, but some (produced in acidic conditions) have low optimum pH

Denaturing enzymes

TEMPERATURE:
-rate increases up to optimum but above it rapidly decreases and stops

-temp too hot = bonds break

-active site shape changes, so substrate can’t fit

PH:
-too high or low = forces holding amino acid chains that make up protein affected
-changes shape of active site, substrate can no longer fit in

Enzymes in digestion

Carbohydrases

Proteases

Lipases

Carbohydrases

Converts carbohydrates into simple sugars

e.g amylase breaks down starch into maltose

Produced in salivary glands, pancreas and small intestine (most starch eaten digested here)

Proteases

convert proteins into amino acids

e.g pepsin (produced in stomach but other forms can be found in pancreas and small intestine)

Lipases

convert lipids into fatty acids and glycerol
produced in pancreas and small intestine

Food tests

-Benedict’s test: sugars (turns brick red)

-Iodine test for starch (turns blue-black)

-Biuret test for protein (turns purple)
-Emulsion test for lipids (ethanol →cloudy layer)

or

-Sudan III test for lipids (red layer forms on top)

Where is Bile produced and stored and released?

Produced in liver
Stored in gallbladder

Released into the small intestine

Roles of bile

1. Alkaline: neutralise hydrochloric acid (comes from stomach). Enzymes have higher (more alkaline) optimum pH than those in stomach

   1. Break down (emulsify) drops of fat. Large SA means lipase can chemically break down lipid →glycerol and fatty acids FASTER!

Role of circulatory system

Carries oxygen and nutrients to every cell in the body, removes waste products

How does the heart pump blood around the body?

In a double circulatory system (there are two circuits)

1. Deoxygenated blood flows into right atrium then into right ventricle - pumps it into the lungs to undergo gaseous exchange

   1. Oxygenated blood flow into left atrium, then left ventricle - pumps oxygenated blood into the body

Heart - structure

-Muscular walls: strong heartbeat
-Left ventricle wall thicker: blood needs to be pumped all around body instead of just lung like right

-4 chambers: separate oxygenated and deoxygenated blood

-Valves: blood doesn’t flow backwards

-Coronary arteries: cover heart to provide its own oxygenated blood supply

Process of heart pumping blood

1. Blood flows into right atrium through vena cava and left atrium through pulmonary vein

2. Artia contract - blood into ventricles

3. Ventricles contract blood pushed into right ventricle into pulmonary artery - taken to lungs, left ventricle to aorta to be taken around body

   4. Valves close to make sure blood doesn’t flow backwards

Natural resting heart rate

70bpm
controlled by group of cells in right atrium (pacemaker - provides stimulation through small electrical impulses which pass as a wave across the heart muscle, causing it to contract)

^ without this, heart wouldn’t pump fast enough to deliver required amount of oxygen

How can someone with an irregular heartbeat be helped?

Artificial pacemaker

Types of blood vessel

Arteries

Veins

CapillariesA

Arteries

Carry blood away away from the heart
-Layers of muscle in walls: make them strong

-Elastic fibres: allow them to stretch

-Helps vessels withstand high pressure created by heart pumping

Veins

Carry blood towards the heart
-Lumen (tube blood flows through): wide so allows low blood pressure to flow through
-Valves: ensure blood flows in right direction

Capillaries

Allow blood flow very close to cells → enable substances to move between them
-One cell thick: short diffusion pathway

-Permeable walls: substances can move across them

Gas exchange system

-Trachea (windpipe, air moves through here)

-Intercostal muscles (contract and relax to ventilate lungs)

-Bronchi (air from trachea move into these, lead to each lung)

-Bronchioles (bronchi split into these and air moves in)

-Alveoli (bronchioles lead to alveoli, air sacs where gaseous exchange occurs)

-Diaphragm (separates lungs from digestive organs, moves down causing inhalation)

Ventilation

1. Ribcage moves up + out, diaphragm moves down (volume of chest increases)

2. Increased volume = lower pressure

3. Air drawn into chest, air moves from areas of high →low pressure (environment to lungs)

4. Opposite happens when exhaling

Gas exchange

1. When inhale, alveoli fill with oxygen

2. Blood in capillaries surrounding alveoli is DEOXYGENATED (come from pulmonary vein) and has lots of carbon dioxide

3. Oxygen diffuses down conc gradient → capillary blood stream (low conc of oxygen)

4. Carbon dioxide diffuses down conc gradient from blood →Alveoli

How are alveoli adapted for gas exchange?

-Small, arranged in clusters (large SA for diffusion to take place over)

-Capillaries provide large blood supply, maintaining conc. gradient
-Walls of alveoli are very thing (short diffusion path)

What is blood made up of?

Plasma, red blood cells, white blood cells, platelets

Plasma

Liquid
Carries components in blood: red blood cells, white blood cells, platelets, glucose, amino acids, carbon dioxide, urea, hormones, proteins, antibodies, antitoxins

Red blood cells

Carry oxygen molecules from lungs to all cells in the body

Bioconcave disc shape: large SA

No nucleus: more room to carry oxygen

Contains red pigment haemoglobin, binds to oxygen and forms oxyhaemoglobin

White blood cells

Part of immune system (body’s defence against pathogens)

Have a nucleus

Different types:

1- Produce antibodies against microorganisms

2-Engulf and digest pathogens

3-Produce antitoxins to neutralise toxins/poisons produced by microorganisms

Platelets

Help blood clot form at site of wound

Clot dries and hardens - forms a scab which allows new skin to grow underneath while preventing microorganisms from entering

Small fragments of cells

No nucleus

Without - cuts result in excessive bleeding and bruising

Coronary heart disease

Occurs when coronary arteries that provide blood become blocked with the build up of fatty material.
Results in less blood flowing to heart - reduces oxygen supply
Non-communicable
May lead to a heart attack

Solutions to coronary heart disease

-Stents
-Statins