Biology Notes

Section 1 — Characteristics and Classification of Living Organisms

Characteristics of Living Organisms
- Living organisms share seven basic characteristics.
- REVISION TIP: Remember "Mrs Gren" (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition).
- Movement: Action causing a change of place or position.
  - Movement can be towards water and food or away from predators and poisons.
  - Plants also exhibit movement.
- Respiration: Chemical reactions in cells breaking down nutrient molecules to release energy for metabolism.
- Sensitivity: Ability to detect and respond to environmental changes (internal or external stimuli).
- Growth: Permanent increase in organism size by cell number, cell size, or dry mass.
- Reproduction: Processes that create more of the same organism.
- Excretion: Removal of metabolic waste, toxic materials, and excess substances.
- Nutrition: Taking in materials for energy, growth, and development.
  - Plants need light, carbon dioxide, water, and ions.
  - Animals need ions, organic compounds, and water.

Classification

Classification: Organising living organisms into groups.
- Organisms are grouped based on shared features.
- Classification helps manage the vast range of shapes, sizes, and physical features of organisms.
Five Kingdom System: Divides living things into five groups.
- Animals: fish, mammals, reptiles, etc.
- Plants: grasses, trees, etc.
- Fungi: mushrooms, toadstools, yeasts, mould.
- Prokaryotes: single-celled organisms without a nucleus.
- Protoctists: eukaryotic single-celled or simple multicellular organisms, e.g. algae.
Species: A group of similar organisms that can reproduce to give fertile offspring.
Binomial System: Internationally agreed system for scientifically naming organisms using their genus and species.
- The first part of the binomial name is the genus, indicating ancestry.
- The second part is the species.
- Example: Homo sapiens (humans), where 'Homo' is the genus and 'sapiens' is the species.

Classification Systems

Classification systems have changed over time with advancements in technology.
Traditional Methods: Classified organisms by morphological and anatomical characteristics.
Modern Methods: Use DNA base sequencing and amino acid sequencing for more accurate classification.
- Organisms sharing a more recent ancestor have more similar DNA base sequences.
- Comparing amino acid sequences in proteins offers a similar approach.
Evolutionary Relationships: Evolutionary trees show relationships between species.
- They show common ancestors and species interrelation.
- Recent common ancestors indicate closer relationships and shared characteristics.

Features of Organisms

Plants and animals are eukaryotic organisms.
Plants
- Multicellular.
- Have chloroplasts for photosynthesis.
- Cells have cell walls made of cellulose.
- Store carbohydrates as sucrose or starch.
- Reproduce sexually or asexually.
Animals
- Multicellular.
- No chloroplasts; eat other organisms for food.
- Cells lack cell walls.
- Most have nervous coordination and can move.
- Store carbohydrates as glycogen.
- Most reproduce sexually.
Cell Components
- Cytoplasm: contains smaller structures and is where reactions happen
- Cell membrane: holds the cell together, responsible for what comes in and out of the cell
- DNA: genetic material responsible for the proteins made within the cell
- Ribosomes: involved in protein synthesis
- Enzymes: involved in respiration
Cells are classified into eukaryotic (with a nucleus) and prokaryotic (without a nucleus).

The Kingdoms

Viruses
- Not living organisms; rely on other organisms to reproduce.
- Particles rather than cells.
- Smaller than bacteria.
- Lack cellular structure but have a protein coat and genetic material (DNA or RNA).
- Reproduce inside living cells (parasites) and are pathogens.
Prokaryotes
- Single-celled, microscopic.
- Lack a nucleus but have a cell wall.
- Possess a circular chromosome of DNA.
- Some can photosynthesise and most feed off other organisms.
- Some are pathogens.
Protoctists
- Mostly single-celled and microscopic.
- Some are multicellular (e.g. seaweed).
- Some have chloroplasts and are similar to plant cells.
Fungi
- Eukaryotic organisms.
- Some are single-celled, others have a mycelium made of hyphae.
- Cannot photosynthesise; feed off other organisms.
- Cells have cell walls made of chitin.
- Store carbohydrate as glycogen.
- Reproduce using spores.

Animal Kingdom

Vertebrates
- Possess a backbone and internal skeleton.
- Divided into five groups: fish, amphibians, reptiles, birds, mammals.
Invertebrates
- Lack a backbone; some have an exoskeleton.
Fish
- Live in water with fins and skeletons of bone or cartilage.
- Have gills and are cold-blooded.
- Lay eggs fertilised externally; some have live births.
Amphibians
- Live on land and in water with moist, permeable skin for breathing.
- Cold-blooded and lay eggs in water for external fertilisation.
Reptiles
- Live on land with dry, scaly skin and lungs.
- Cold-blooded and mostly lay eggs.
Birds
- Have feathers and wings; most fly with beaks and lungs.
- Warm-blooded and lay eggs.
Mammals
- Have hair or fur and sweat glands with lungs and external ears.
- Warm-blooded and mostly give birth to live young.
- Females produce milk from mammary glands.

Types of Arthropods

Arthropods are invertebrates with exoskeletons and segmented bodies.
Myriapods: many legs, one pair of antennae.
Insects: three pairs of legs, three-part body (head, thorax, abdomen), one pair of antennae, and usually wings.
Arachnids: four pairs of legs, two-part body (head/thorax, abdomen), no antennae or wings.
Crustaceans: mostly aquatic, jointed legs, some branched limbs, two pairs of antennae, no wings.
Flowering Plants: reproduce using flowers and seeds. Can be divided into monocotyledons or dicotyledons.
Monocotyledons: one cotyledon, petals in multiples of three, parallel leaf veins.
Dicotyledons: two cotyledons, petals in multiples of four or five, branching leaf veins.

Dichotomous Keys

Dichotomous keys are used to identify organisms based on their features.
Repeatedly divide organisms into two categories with questions or statements.
To construct a key:
- Start with a sample of organisms.
- Split the sample into two groups based on one characteristic.
- Write statements describing each group.
- Split each group into two using a different characteristic.
- Continue until left with pairs, then link statements in the correct order.

Section 2 — Organisation of the Organism

Cells
- The basic building blocks of all life.
- Animal Cells
  - Nucleus: contains genetic material and controls the activities of the cell
  - Cytoplasm: gel-like substance where most chemical reactions happen
  - Cell membrane: holds the cell together and controls what goes in and out
  - Mitochondria: where most of the reactions for aerobic respiration take place
  - Vesicles: fluid-filled sacs surrounded by a membrane, transport substances in and out of the cell
  - Rough Endoplasmic Reticulum:almost all eukaryotic cells have this
- Plant Cells
  - Rigid cell wall
  - Chloroplasts: where photosynthesis occurs
  - Vacuole: contains cell sap
Specialized Cells
- Cells that have a structure which makes them adapted to their function
- Palisade mesophyll cells: Specialised for Photosynthesis
- Root Hair cells: Specialised for Absorbing Water and Minerals
- Xylem Cells: Specialised for Transporting Water
- Ciliated Cells: Specialised for Moving Materials
- Red Blood Cells: Specialised to Transport Oxygen
- Nerve cells: Specialised for Impulse Conduction
- Sperm and Egg Cells: Specialised for Reproduction

Levels of Organisation

Tissues: Groups of similar cells performing a shared function.
- Muscular tissue, for example, contracts for movement.
Organs: Groups of different tissues working together for specific functions.
- Lungs and leaves are examples of organs.
Organ Systems: Groups of organs working together to perform body functions.
- The urinary system is an example.
Magnification: Microscopes magnify images using lenses.
magnification = \frac{image \ size}{real \ size}
Units conversion:
- Kilometre (km) (\times 10^{3} m)
- Millimetre (mm) (\times 10^{-3} m)
- Micrometre (µm) (\times 10^{-6} m)
- Nanometre (nm) (\times 10^{-9} m)
- Picometre (pm) (\times 10^{-12} m)
Formula triangle is used to calculate magnification.

Section 3 — Movement In and Out of Cells

Diffusion
- The gradual movement of particles from places where there are lots of them to places where there are fewer of them.
- Diffusion happens in both solutions and gases.
- Requires kinetic energy, no additional energy from cells to make it happen.
- Cell membranes and diffusing particles
- Diffusion is the net movement of particles from a region of their higher concentration to a region of their lower concentration as a result of their random movement.
  - Concentration gradient
Factors that affect Rate of diffusion
- Surface area
- Temperature
- Concentration gradient
- Distance
Phenolphthalein is a pH indicator — it’s pink in alkaline solutions and colourless in acidic solutions
Investigating rate:
- To investigate the effect of distance on rate, you’ll need to carry out a slightly different experiment:
  1) Fill two identical beakers with different volumes of water, e.g. 100 cm^{3} and 250 cm^{3}.
  2) Once the water is still, add a couple of drops of ink to each beaker.
  3) Time how long it takes for the ink to spread out completely in each beaker.
Osmosis
- Water diffuses through partially permeable membranes by osmosis.
- Partially permeable membranes have very small holes in it.
- Sucrose solution
  - Net movement of water molecules
- Pure water has the highest water potential. All solutions have a lower water potential than pure water.
- The net movement of water molecules from a region of higher water potential to a region of lower water potential, across a partially permeable membrane.
Investigating Osmosis
- Experiment to see what effect different water concentrations have on potato.
- Potato cylinder in varying concentrations of sugar solution.
Water always moves into the more concentrated solution
Osmosis Affects Plant Cells too
- If a plant cell is placed in a solution with a higher concentration of water molecules than the solution inside the plant cell, water will move into the cell by osmosis. This will make the cell become plump and swollen.
A plump and swollen cell is called a turgid cell
A limp and wilted cell is called a flaccid cell
If the plant’s really short of water, the cytoplasm inside its cells starts to shrink and the membrane pulls away from the cell wall. This process is called plasmolysis.
Active Transport
- Active transport is the movement of particles across a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration.
- protein molecules called carrier proteins are involved in active transport.
- Plants need mineral ions for healthy growth.
- Glucose can be taken into the bloodstream when its concentration in the blood is already higher than in the gut.

Section 4 — Biological Molecules and Enzymes

Biological Molecules
- Carbohydrates: Made of simple sugars
- Proteins: Made Up of Long Chains of Amino Acids
- Fats and Oils: Made Up of Fatty Acids and Glycerol
Proteins Have Many Different Functions
- ENZYMES — act as biological catalysts to speed up chemical reactions in the body.
- ANTIBODIES — are part of the immune system and help the body fight pathogens
You Can Test for Sugars Using Benedict’s Solution
* blue green yellow orange brick red
The Biuret Test is Used for Proteins
* the solution will stay blue solution will turn purple.
Starch is Tested for with Iodine
* the sample changes from browny-orange to a dark, blue-black colour. the solution will stay browny-orange.
Use the Ethanol Emulsion Test for Fats and Oils
* Test substance and ethanol
* Shake add to water
* Milky Colour indicates fat
Use the DCPIP Test for Vitamin C
- DCPIP solution drop by drop to a food sample containing vitamin C
  - bllue to colourless means presence of vitamin C
  - Keep adding DCPIP until the blue colour no longer disappears when it’s mixed with the sample.
  - The more fats or oils present, the more noticeable the milky colour will be.
  - double stranded helix
  - Water is Important as a Solvent
Enzymes
Enzymes are Proteins that Act as Catalysts
An Enzyme’s Shape Lets it Catalyse Reactions
- substrate molecule binds to an enzyme, it is changed to a product and then released.
- enzyme substrate active site products enzyme unchanged after reaction enzyme-substrate complex
  - enzyme substrate active site products
  - Enzymes Like it Warm but Not Too Hot
  - Enzymes Also Need the Right pH
    Enzymes Also Need the Right pH
  - pH optimum pH Rate of reaction
  - You can Investigate Factors that Affect Enzyme Activity
    dropping pipette drop of iodine solution mixture sampled every 10 seconds spotting tile starch solution and amylase enzyme solutions (at correct temperature) mixed and placed in water bath well

Section 5 — Plant and Human Nutrition

Photosynthesis
- Photosynthesis is the process that plants use to manufacture carbohydrates (glucose) from raw materials(carbon dioxide and water) using energy from light.
- LIGHT 6CO2 + 6H2OC6H{12}O6+6O2
  - Plants Use Glucose in Five Main Ways
    for respiration is important
    Making cellulose
    Making amino acids
    Stored as fats or oils
Rate of Photosynthesis
- The Temperature Has to be Just Right Rate of photosynthesis.
  - Too Little CO2 Slows Down the Rate of Photosynthesis
    % level of CO2 Rate of photosynthesis
You can Investigate Photosynthesis
Oxygen Production Shows the Rate of Photosynthesis
* You Need to Know How to Test a Leaf for Starch
hydrogencarbonate Indicator Shows CO2Concentration
Improving Plant Growth
You can Create the Ideal Conditions for Photosynthesis
The Rate of Photosynthesis Affects Plant Growth
You can use glasshouses to control the growing environment
Leaf Structure and Mineral Requirements
Leaves are Adapted for Efficient Photosynthesis