What are cells?
The small building blocks that make up all living organisms.
State the functions of the ‘cell membrane’
- Forms a barrier between the cell and its surrounding
- Keeps contents to cell inside
- Allows simple substances to enter and leave the cells, e.g. oxygen, carbon dioxide and water
- Controls movement of other substances into and out of the cell, e.g. glucose
- Often described as partially permeable
State the functions of the ‘nucleus’
- Controls all activities in the cell
- Controls how cells develop
State the functions of the ‘cytoplasm’
- Place where many chemical reactions take place, e.g. respiration and making proteins for the cell
State the functions of the ‘chloroplast’
- Photosynthesis
- Stores starch
State the functions of the ‘cell wall’
- Stops cells from bursting when they fill with water
- Gives shape to cells
- Allows water and dissolved substances to pass through freely (often described as freely or fully permeable)
State the functions of the the ‘vacuole’
- Full of water to maintain shape and ‘firmness’ of cell
- Stores salts and sugars
How to calculate the magnification?
Image size / Actual size
Describe the structure of an animal cell
- Contains a cell membrane, nucleus, cytoplasm, mitochondrion
Describe the structure of a plant cell (palisade)
- Contains a cell wall, cell membrane, vacuole, cytoplasm, nucleus, chloroplasts`
Adaptations of root hair cells to its function
- Long extensions that give them a large surface area to absorb water from the soil.
- Thin cell walls - shorter distance for diffusion
Adaptations of ciliated cells to its function
- Found in air passages in the lungs (trachea and bronchi)
- Beat back and forth to create a current in the fluid next to the cell surfaces.
- Move mucus that traps dust and pathogens up to the nose and throat.
Adaptations of red blood cells to its function
- Contain protein haemoglobin that carries oxygen.
- Biconcave shape - provides large SA compared with their volume which makes it efficient to absorb oxygen.
Describe the levels of organisation
Cells -> tissue -> organs -> organ system
Define ‘diffusion’
The net movement of molecules from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement.
Name the factors that affect diffusion
- Distance (the shorter the better) e.g. thin walls of alveoli and the capillaries.
- Concentration gradient (the bigger the better). This can be maintained by removing the substance as it passes across the diffusion surface.
- Size of the molecules (the smaller the better).
- Surface area for diffusion (the larger the better) e.g. there is millions of alveoli in a lung, giving a huge surface area for diffusion of oxygen.
- Temperature (molecules have more kinetic energy at higher temperatures).
Describe the importance of diffusion of gases and solutes and of water as a solvent
- Oxygen: from alveoli -> blood capillaries
- Carbon dioxide: from blood capillaries -> alveoli; from air -> stomata into leaf for photosynthesis
- Soluble food products from digestion: from small intestine -> blood capillaries
- Scent made of tiny molecules: flowers -> bee’s body
Define ‘osmosis’
The diffusion of water molecules from a region of their higher concentration (dilute solution) to region of their lower concentration (concentrated solution), through a partially permeable membrane.
Describe the importance of osmosis in the uptake of water in plants
- Usually, the water in the soil is more dilute than that in root hair cells
- So water enters root hair cells by osmosis (a passive process – requiring no energy)
Describe the effects of osmosis on plant and animal cells
- When placed in pure water, plant and animal cells will take in the water by osmosis;
- This is because there is a higher concentration of water molecules outside the cell than inside it;
- Plants become turgid, but do not burst because of their tough cell wall;
- Animal cells will burst, because they have no cell wall;
- The reverse happens when plant and animal cells are placed in a concentrated sugar or salt solutions. This is because there is a higher concentration of water molecules inside the cell than outside it;
- Plant cells become flaccid and the cytoplasm is no longer pressed against the cell wall;
- Animal cells also become flaccid and their shape changes- they can become crenated.
Describe and explain the importance of a water potential gradient in the uptake of water by plants.
- Water potential is the correct term for saying ”water concentration” a high water potential is equivalent to a low solute concentration and vice versa;
- For plants to take in water through their roots they must have a high solute concentration or low water potential in the roots and low solute concentration or high water potential outside the roots.
- In osmosis, water molecules diffuse down a water potential gradient.
