a) Levels of organisation
2.1 describe the levels of organisation within organisms: organelles, cells,
tissues, organs and systems.
Living organisms are made up of cells. Some organisms only consist of a single-cell, and others are multicellular and contain lots of cells. There is an order of organisation for these cells.
In order of increasing complexity;
organelle - cell - tissue - organ - organ system.
Organelle - These are tiny structures within cells. They can only be seen when using a powerful microscope as they are so small. They are cell structures that are specialised to carry out a particular function or job.
Cell - Cells are also specialised to carry out a particular function, so their structures can vary. An example of this are the red blood cells found in humans, that are specialised in carrying oxygen.
Tissue - A tissue is a group of cells with similar structures that work together to perfom a specific function. A group of tissues that also works together to perform a specific function would be an organ.
Organ - An organ is a group of tissues that work together to perform a function. An example of an organ would be leaves on plants or lungs in mammals.
Organ System - Group of organs with related functions. Organs work together in organ systems, and each system does a different job. An example of an organ system is the digestive system that can be found in mammals. The digestive system is made up of organs such as; the stomach, intestines, pancreas and liver.
b) Cell structure
2.2 describe cell structures, including the nucleus, cytoplasm, cell membrane,
cell wall, chloroplast and vacuole
2.3 describe the functions of the nucleus, cytoplasm, cell membrane, cell wall,
chloroplast and vacuole
Animal and plant cells have certain structures in common, these are;
Nucleus: an organelle which contains genetic material that controls it's activities. It is surrounded by the cell membrane.
Cytoplasm: this is a gel-like substance where most of the cell's chemical reactions happen. It contains enzymes, which control these reactions.
Cell membrane: this forms the outer surface of the cell and controls the substances that go in and out.
Plant cells also have additional structures that they do not share with animal cells;
Cell wall: This is a hard structure made of cellulose that surrounds the cell membrane. It supports the cell and strengthens it.
Chloroplast: It is here that photosynthesis happens, which makes food for the plant. Chloroplasts contain a green substance called chlorophyll, which is used in photosynthesis.
Vacuole - Both plant and animal cells can have these, however they are never permanent in animal cells, but they always are in plant cells. It is a large organelle that contains cell sap, which is a weak solution of sugars and salts that help to support the cell.
2.4 compare the structures of plant and animal cells.
Differences between the two;
- Plant cells have additional structures in their cells that animal cells do not.
- These include: chloroplasts, cell wall, and vacuole.
- However, some animal cells do have a vacuole, but these are never permanent like they are in plant cells.
Similarities between the two;
- Both have nuclei.
- Both have cytoplasm.
- Both have a cell membrane.
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