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Revision End of Year - Biology 2025 - Coggle Diagram
Revision End of Year - Biology 2025
Topic 1 - Organisation Cells and Microscopy
Cells are basic building blocks of all living organisms
A tissue is a group of cells
Organs are groups of tissue that have a specific function
Organ Systems are groups of organs that work together to make stuff happen
An organism is made up of Organ systems that help it live
Cells
Eukaryotic Cells
Plant and animal cells are eukaryotic - they have a cell membrane, cytoplasm and genetic material (DNA) enclosed in a nucleus
Prokaryotic Cells
Much smaller then Eukaryotic
They have cytoplasm and a cell surrounded by a cell wall
The DNA is not enclosed in the nucleas
Sub-cellular Structures
In all cells
A nucleus that controls the cell
Cytoplasm is where the reactions take place
Cell membrane controls what comes in or out of the cell
Mitochondria is where aerobic respiration takes place
Ribosomes store and use proteins
Also in plant cells
Chloroplasts absorb light to make food by photosynthesis
A vacuole filled with cell sap, which supports the cell
A cell wall made of cellulose to strengthen the cell
Specialised Cells
What is it?
Specialised cells are cells designed to carry out a particular role in the body, such as red blood cells which are designed to carry oxygen.
Different specialised cells
Plant Specialised Cells
Xylem Cells - Transports water and minerals from the roots up the plant stem and into the leaves
Phloem Cells - Moves food substances that the plant has produced by photosynthesis
Root Hair cells - Absorb water and minerals from soil by osmosis
Animal Specialised Cells
Sperm Cells - Fertilise an egg cell to pass on your DNA
Muscle Cells - Responsible for practically all movements that are under voluntary control
Nerve Cells - Receives and sends messages from the body to the brain and back to the body
Microscopy
Calculations involving magnification
Magnification = size of image / size of real object
Rearrange the equation to calculate image size or magnification
Values
Milli - mm
Micro - µm
Centi - cm
Nano - nm
From cm to mm = x10
From mm to µm = x1000
From µm to nm = x1000
Express answers in standard form if appropriate
REQUIRED PRACTICAL 1 - Using a microscope to observe and draw cells
How to produce a slide
Peel away or cut a very thin layer of cells to go on the slide
Gently place a cover slip on top and press down to remove any air bubbles
Place the slide onto the stage of the microscope
How to focus a microscope
Start by rotating the objective lens to lowest power.
Place a slide on the stage, label side up, with the coverslip centered.
Use the coarse focus knob to get the object into focus.
If you cannot see anything, move the slide slightly while viewing and focusing.
Things to remember when drawing scientificly
Use a pencil
Try fill the page
Solid lines - not feathery sketch lines
Don't shade
Use a ruler for label lines
Don't overlap label lines
Include magnification and title on your drawing
An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.
Topic 2 - Respiration
Aerobic Respiration (With Oxygen)
Takes place in Mitochondria
It is respiration in cells to transfer energy with oxygen
Equation for Aerobic Respiration...
glucose + oxygen → carbon dioxide + water + energy release
C6H12O6 + O2 = CO2 + H2O + Energy Release
Anaerobic Respiration (Without Oxygen)
Equation in muscles...
Glucose → Lactic Acid
Equation in plants and yeast...
Glucose → Ethanol + Carbon Dioxide + Energy Release
This is called fermentation
Why do they need energy?
Movement
Keeping warm
Chemical reactions to build larger molecules
During exercise the human body reacts to the increased demand for energy.
Breathing rate increases
Breath volume increases
Heart Rate increases
These are needed to supply muscles with more oxygenated blood
This means more cells respiration, so more energy is transferred
If not enough oxygen is supplied then anaerobic respiration will take place
This causes oxygen debt
Which means after long exercise periods somebody's muscles could become more fatigued and stop contracting efficiently
Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.
Compare...
As the oxidation of glucose is incomplete in anaerobic respiration much less energy is transferred than in aerobic respiration.
The relative amount of energy transferred in Aerobic Respiration is a large amount
The relative amount of energy transferred in Anaerobic Respiration is a small amount but a bit quicker
Metabolism
The sum of all the reactions in a cell or in the body
The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules.
Metabolism includes:
Conversion of glucose to starch
The formation of lipid molecules
Breakdown of excess proteins to form urea for excretion
The use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins
Respiration
Topic 3 - Transport in Cells
DIffusion
Substances may move into and out of cells across the cell membranes via diffusion
Diffusion is the spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration
Different factors affect the rate of diffusion:
The temperature
The surface area of the membrane
A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism
How to calculate the surface area to volume ratio:
The surface-area-to-volume ratio tells you how much surface area there is per unit of volume
To find surface area, find the area of each side and add them together
To find volume, height × width × depth
Difference in concentration
Exchange surfaces
They are specialized structures in the body that allow for the exchange of materials between the body and the environment
We need them to allow the body to take in oxygen and nutrients from the environment, and to eliminate waste products
The effectiveness of an exchange surface can be changed by the following...
A large surface area
A membrane that is thin to provide a short diffusion pathway
Efficient ventilation
An efficient blood supply
Adaptations that show this include:
Gills in fish - many filaments
Roots in plants - root hair cells
The lungs in mammals (trachea, bronchi, alveoli, capillary network surrounding alveoli)
Leaves in plants
The small intestine in mammals - villi and microvilli
Transport systems
They are a system of tubes with a pump and valves to ensure one way blood flow
Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
Effect of Osmosis on plant cells
Plant cells placed in a solution with a high water concentration compared to their contents (eg pure water) will gain water by osmosis and swell up until their cytoplasm and cell membrane are pushing against their cell wall
This is called turgid when a cell changes shape
Effect of Osmosis on animal cells
Red blood cells placed in a solution with a higher water concentration compared to their contents (eg pure water) will gain water by osmosis, swell up and burst. Water will diffuse from a higher water concentration outside the cell to a lower water concentration inside the cell.
RP3: Osmosis - Investigate the effect of a range of sugar concentrations on the mass of plant tissue
Method for Practical:
Active Transport
Moves substances from a more dilute solution to a more concentrated solution, against a concentration gradient
This requires energy from respiration
Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth
Active transport allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration
What is the difference between Diffusion, Osmosis and Active Transport?
Osmosis is the diffusion of water across a membrane
Active transport moves particles from low to higher concentration
Diffusion is the movement of particles from a high to lower concentration
Topic 4 - Digestive System
The digestive system is an example of an organ system in which several organs work together to digest and absorb food.
Different types of digestion
Physical Digestion
This is the actual physical things that the body is doing
Stomach Churning
Mouth Chewing
Chemical Digestion by enzymes:
Are large proteins
Catalyse a specific reaction due to the shape of the active site being complementary to the shape of one specific substrate
Are biological catalysts (Speed up chemical reactions)
Are denatured by high temperatures (Their shape changes so then they can't fit to the substrate and can't react)
Have an optimum temp
Have an optimum PH
Enzymes can be shown by a simple diagram called the lock and key diagram
In reality the active site changes shape a bit as the substrate binds to it. This enables a tighter fit, and is called the induced fit model
Digestive enzymes convert large food molecules into small soluble molecules that can be absorbed into the bloodstream
Enzymes also link to metabolism:
The products of digestion are used to build new carbohydrates, lipids and proteins
Some glucose is used in respiration
Absorbtion in the Small Intestine:
One cell thick lining: short distance for absorption by diffusion / active transport
Good blood supply: maintains a steep concentration gradient
Very long, villi, microvilli: provide a large surface area
Bile
Bile is made in the liver and stored in the gallbladder.
It is alkaline to neutralise hydrochloric acid from the stomach
It also emulsifies fat to form small droplets which increases the surface area
The alkaline conditions and large surface area increase the rate of fat digestion by lipase
RP5: Effect of PH on enzyme action:
