B1 - Cells and Organisms
B1.1
1km = 1000m, 1m = 100cm, 1cm = 10 mm, 1mm = 100um, 1um = 1000 nm
Light microscopes use a beam o flight to form an image of an object and the best can magnify around 2000 times (X200).
To calculate the size of an object, Magnification = size of image / size of real object
Light microscopes magnify up to X20000, and have a resolving power of about 200nm.
Electron microscopes magnify up to X2000000, and have a resolving power of around 0.2nm.
B1.2 Animal and Plant cells
Animal cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant and algal cells have the same as animal cells, as well as a cellulose cell wall.
Many plant cells also contain chloroplasts and a permanent vacuole filled with sap.
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Cell part - Function - Plant or animal cells?
Cell membrane Controls what goes in and out of the cell both
Nucleus Carries genetic material and controls what the cell does both
cytoplasm A jelly like substance where most of the chemical reactions take place both
mitochondria This is where respiration takes place both
ribosomes This is where protein synthesis takes place both
vacuole contains cell sap and keeps the cell in shape Plant cell
chloroplasts Needed for photosynthesis and contains chlorophyll Plant cell
Cell wall Supports and protects the plant cell and it is made of cellulose Plant cell
B1.3 Eukaryotic and Prokaryotic cells
Eukaryotic cells all have a cell membrane, cytoplasm, and genetic material enclosed in the nucleus. The genetic material is the DNA and it forms structures called chromosomes that are contained within the nucleus. E.g. Animal and plant cells
Prokaryotic cells consist of cytoplasm and a cell membrane surrounded by a cell wall. The genetic material is not in a nucleus. It forms a single DNA loop. Prokaryotes may contain one or more extra small rings of DNA called plasmids.
Bacteria are all prokayotes
Eukaryotic cells are bigger then prokaryotic cells.
Flagella are long protein strands out the back of a prokaryotic cell. They help the cell move around.
B1.4 Specialisation in animal cells
As an organism develops, cells differentiate to form different types of specialized cells. Most, at an early stage of life.
As a cell differentiates, it gets different sub-cellular structures that enable it to carry out a particular function. It has become a specialized cell.
Examples of specialised animal cells include: Nerve cells, Muscle cells, and sperm cells.
Nerve cells are specialized to carry electoral impulses around the body of an animal. They have lots of dendrites to make connections to other nerve cells. The axon carries the nerve impulse from one place to another. The nerve endings (synapse) are adapted to pass the impulses to another cell.
Muscle cells are specialized to contract and relax. They work together in tissues called muscles. Muscles contract and relax in pairs to move the bones of teh skeleton, so vertebrates can move on land and water, and in some cases fly.
Striated muscle cells have three main adaptations: They contain special proteins that slide over each other making the fibers contract. They contain many mitochondria to transfer the energy needed for the chemical reactions that take place as the cells contract and relax. They can store glycogen .
Animal cells may be specialized to function within a tissue, an organ, organ systems, or whole organisms.
B1.5 Specialization in plant cells
Plant cells may be specilised to carry out a particular function
Examples of specialized plant cells include root hair cells, photosynthetic cells, xylem cells, and phloem cells.
Root hair cells - they are found close to the tips of growing roots. Plants need to take in lots of water, and dissolve mineral ions. The root hair cells help them do this more efficiently. Root hair cells are normally close to the xylem tissue, which carries water and mineral ions up into the rest of the plant. Mineral ions are moved into the root hair cell by active transport.
Photosynthetic cells - they make the plants food by photosynthesis. Photosynthetic cells have a few adaptations:
Xylem cells - Xylem is the transport tissue in plants that carried water and mineral ions from the roots to the highest leaves and shoots. The xylem is also important in supporting the plant. It is made up of xylem cells that are adapted to their functions in two main ways.
They contain specialized green structures called chloroplasts contain chlorophyll that trap the light needed for photosynthesis
They are usually positioned in continues layers in the leaves and outer layers of the stem of a plant so they absorb as much light as possible
They have a lot of large permanent vacuole that helps keep the cell rigid as a result of osmosis. when lots of these rigid cells are arranged together to form a photosynthetic tissue, they help support the stem. They also keep the leaf spread out so it can capture as much light as possible.
The xylem cell are alive when they are first formed but a special chemical called lignin builds up in spirals in teh cell walls. The cells die and form long hollow tubes that allow water and mineral ions to move easily through them, from one end to the plant to the other.
The spirals and rings of lignin in the xylem cells make them very strong and help them withstand the pressure of water moving up the plant. They also help support the plant stem.
Phloem cells - phloem is the specialized transport tissue that carries food made by photosynthesis around the body of the plant. It is made up of phloem cells that form tubes rather like xylem cells, but phloem cells do not become lignified and die. The dissolved food can move up and down the phloem tubes to where it is needed.
The cell walls between the cells break down to form special sieve plates. These allow water carrying dissolved food to move freely up and down the tubes to where it is needed.
Phloem cells lose a lot of their internal structures but they are supported by companion cells that help to keep them alive. The mitochondria of the companion cells transfer the energy needed to move dissolved food up and down the plant in phloem.
B1.6 Diffusion
Diffusion is the spreading out of particles of any substance, in a solution or a gas. This results in a net movement from an area of higher concentration to an area of lower concentration, down a concentration gradient. The motion of all the particles causes them to bump into each other, and this moves them all around.
If there is a big difference in concentration between two areas, diffusion will take place quickly. Many particles will move randomly towards the area of low concentration, and only a few in the other direction
On the other hand, if there is only a small difference in concentration between two areas, the net movement by diffusion will be quite slow. The number of particles moving into the area of low concentration by random movement will only be slightly more than than the number of particles that are leaving the area.
In general, the greater the difference in concentration, the faster the rate of diffusion. This difference is called the concentration gradient. The bigger the difference, the steeper the concentration gradient and the faster the rate of diffusion
Diffusion occurs down a concentration gradient
Temperature also affects the rate of diffusion. The higher the temperature, the move quickly the particles will move around. When this happens, diffusion takes place more rapidly as the random movement of the particles speeds up.
Dissolved substances move in and out of your cells by diffusion across the cell membrane. E.g. sugars such as glucose, gases such as oxygen and CO2, and waste products such as urea from the breakdown of amino acids in your liver.
The oxygen you need for respiration passes from the air in your lungs into your red blood cells through the cell membranes through diffusion. It moves from high-low gradient