Paper 1 Notes

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