Key Concepts in Biology

Cells

Organelles - subcellular structures

Eukaryotic - with nucleus:

• Animal cells

  • Nucleus - DNA, controls

  • Cytoplasm - contains enzymes, where most reactions happen

  • Mitochondria - respiration

  • Ribosome - protein synthesis

  • Cell membrane - controls what goes in and out of the cell

• Plant cells

  • Nucleus - DNA, controls

  • Cytoplasm - contains enzymes, where most reactions happen

  • Mitochondria - respiration

  • Ribosome - protein synthesis

  • Cell membrane - controls what goes in and out of the cell

  • Cell wall - strengthens cell

  • Vacuole - sac filled with cell sap

  • Chloroplasts - photosynthesis, contains chlorophyll

Prokaryotic - without nucleus:

• Bacterium

  • Plasmid - where DNA is held since the cell has no nucleus

  • Flagellum - movement

  • Cell membrane - controls what goes in and out of the cell

  • Cytoplasm - contains enzymes

  • Ribosomes - protein synthesis

  • Chromosomal DNA - contains most of the genes

  • Mesosome

Specialised Cells

• A cell that goes through differentiation to be able to carry out one specific purpose

Examples:

• Sperm

  • Flagellum - tail to swim

  • Nucleus

  • Long mitochondria - needs energy to swim to the egg

  • Acrosome - helps sperm penetrate the egg’s jelly coat

  • Plasma membrane

• Egg

  • Cell membrane

  • Mitochondria

  • Cytoplasm

  • Haploid nucleus

  • Thick jelly coat that hardens when a sperm gets in so that no more can enter

• Ciliated cells

• Red blood cells

• Nerve cell

• Xylem cell

• Root hair cell

Microscopes

Magnification = objective lens x eyepiece lens

Micrograph - image that a microscope creates

Stage - what the slide sits on

Coarse adjustment - higher dial that roughly makes the image clearer

Fine adjustment - lower dial that makes the image fully clear

Eyepiece lens - smaller magnification

Objective lens - larger magnification

How many um are there in a mm?

1000um

How many nm are there in a um?

1000nm

How to Prepare a Slide

1. Place sample on the slide

2. Stain with iodine

3. Place coverslip on sample

4. Place slide on stage

5. Select objective lens

6. Use rough focus knob

7. Use fine focus knob

Enzymes

• Made of protein

• Biological catalyst

Substrate - what it works on

Active site - what the substrate binds to to break it down

Catalyst - something that speeds up a reaction

Biological catalyst - something that speeds up a reaction without being used up itself

Lock and Key Mechanism:

1. Substrate enters active site

2. Enzyme-substrate complex formed

3. Reaction happens

4. Product leaves active site

Digestive enzymes - break down large food molecules down to ones small enough to absorb

• Amylase - starch (carbohydrate) → glucose

  • In saliva, small intestine, pancreas

• Protease - protein → amino acids

  • In stomach, small intestine, pancreas

• Lipase - fat → fatty acids and glycerol

  • In small intestine, pancreas

Denaturing - active site has changed shape

Caused by → high temperature, low/high pH

Experiment to see what happens when different pHs are used:

1. Warm one test tube of starch solution and one test tube of amylase and pH buffer to 40 degrees

2. Mix tubes and start timer

3. Every 30s, remove a small sample, put it in one well of a spotting tile and test the pH with iodine

4. Record time when no colour change

5. Repeat with different pHs

Diffusion, Osmosis, Active Transport

Concentration - number of particles in a given volume

• Diffusion - when molecules move from a high concentration to a low concentration (down a concentration gradient)

• Osmosis - diffusion of water across a partially permeable membrane

• Active Transport - movement of any substance from a low to high concentration (up a concentration gradient)

Investigating Osmosis:

1. Cut potatoes into cylinders of equal size

2. Blot them dry

3. Measure them

4. Record mass

5. Place them in sucrose solutions of different concentrations

6. Leave for 15 mins

7. Blot them dry

8. Reweight them

9. Calculate the percentage change

Cells and Control

Cell Division

• The process of making 2 cells

Diploid - contains 23 pairs of chromosomes

Haploid - contains 23 chromosomes

Mitosis:

• One diploid parent cell

• Two genetically identical daughter cells

• Asexual reproduction

• Growth and repair

• Makes all cells except gametes

1. Interphase (before mitosis) - copying chromosomes and cell grows - preparation for mitosis

2. Prophase - nucleus breaks down, spindle fibres form

3. Metaphase - spindle fibres are fully formed and are lined up along the equator

4. Anaphase - pairs pulled to opposite poles

5. Telophase - new nucleus forms around each end, cell pinches in the middle

6. Cytokinesis (after mitosis) - separation of cells is completed

Meiosis:

• Two haploid parent cells

• Four genetically different daughter cells

• Sexual reproduction

• Used to make only gametes

• Starts in a similar way to mitosis

• Daughter cells split without replicating chromosomes

Egg - ovum

Egg + sperm → zygote → embryo → fetus → baby

Stem Cells

Stem cells - cell that can differentiate

Differentiation - when a cell divides to produce 2 types of specialised cell

Nervous System

Sensory - carries impulse to central nervous system

Relay - makes decisions

Motor - carries impulse from central nervous system to muscle

Reflex Arc:

stimulus → receptor → sensory → relay → motor → muscle

Allows an automatic reaction to keep us safe - doesn’t involve the brain - relay neurone makes decision

DNA

Chromosome - large piece of DNA

Gene - section of DNA

Structure:

• Double helix

• Complementary base pairs

• Sugar phosphate backbone

• Bases are held together by weak hydrogen bonds

• Bases attached to sugar

Alleles

Can be:

• Dominant - one copy needed to show feautre

• Recessive - 2 copies needed to show feature

• Homozygous - 2 of the same allele

• Heterozygous - different alleles

• Phenotype - what you see

• Genotype - genes you have

Capital letter shows dominant allele

Lowercase letter shows recessive allele

Each parent gives one allele

Variation

• Differences between members of a species - effects chances of survival

Discontinuous - genes

Continuous - genes and environment

Natural Selection and Genetic Modification

Selective Breeding

• Improving characteristics of crops or animals

1. Select individuals with the best characteristics

2. Breed them

3. Raise their offspring

4. Breed the best of those together

5. Repeat

Can lead to issues with inbreeding

Genetic Engineering

• Inserting genes from one organism into another

1. Remove desired gene from the chromosome

2. Cut organism’s chromosome open using a restriction enzyme

3. Insert into organism using DNA ligase

4. Breed organism (offspring will contain new gene)

Evolution

• Theory by Charles Darwin

• Radiometric dating gives an age in years for rocks by measuring carbon-14, which is radioactive

• Common ancestor - ancestor shared by 2 or more other organisms

Classification

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Makes genetically modified organism (GMO)

Health and Disease

Non-communicable Diseases

Malnutrition - getting too much/too little of certain nutrients

• Obesity - too much nutrients

  • Too much fat/carbohydrates

• Nutrient deficiency - too little nutrients

  • Kwashiorkor

  • Scurvy - lack of vitamin C (swollen, bleeding gums, bone issues)

  • Rickets - softens bones and curves them - lack of vitamin D or calcium

  • Anaemia - caused by lack of iron (lightheadedness)

Liver disease

Caused by alcohol abuse

• Cirrhosis - liver starts to break down

  • Causes death

  • Only cure is to get a liver transplant

Cardiovascular Disease

• Caused by obesity

• Non-communicable disease

• Heart disease

• Determine obesity by BMI

BMI = mass (kg)/height^2 (m)

Heart attacks - inside arteries, plaque builds up, blocks arteries, blood can’t get through, body doesn’t get as much nutrients, heart can die and the rest of the body stops getting nutrients

Prevented by exercise and healthy lifestyle

Communicable Diseases

Pathogens - microorganisms that cause disease

Types of Pathogen:

• Bacteria

• Virus

• Protist

• Fungus

Cholera - bacteria (vibrio cholera) - waterborne

TB - bacteria (mycobacterium tuberculosis) - airborne

Malaria - protist - vector (mosquitos)

Chalara ash dieback - fungus - airborne

Cold/flu - virus - airborne

Food poisoning - bacteria - oral route

HIV - virus - sexually transmitted

Ebola - virus - direct contact

Immune System

• Kills/destroys pathogens

Immune response:

• Antigens are on pathogens

• Antibody has a shape that matches antigens and marks it

• Antitoxin finds antibody and kills pathogen

Lymphocyte produces antibodies

Phagocyte - phagocytosis (engulfing of pathogens)

• Most lymphocytes will die

• Memory lymphocytes will remain to remember the pathogen when it returns - making you immune