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Cell Structure and
Organisation
All living things are made up of cells. Prokaryotes are (usually) unicellular without a nucleus or other membrane bound organelles. For example: bacteria. Eukaryotes are (usually) multi cellular and contain a nucleus and membrane bound structures. Examples include; animals, plants, fungi and protists. I. Animal Cells
Animal cells contain ; Cell Membrane: A thin skin layer around the cell to give it its shape and control what enters and exits the cell. Cytoplasm: A jelly-­‐like substance in which most of the chemical reactions needed for life take place. Mitochondria: Structures within the cytoplasm where oxygen is used and energy is released during respiration. Nucleus: Controls what the cell does. Contains the DNA, which carries the instructions for making new cells. Ribosome: Where protein synthesis takes place. All the proteins needed in the cell are made by these structures. II. Plant Cells
Plant Cells contain all of the above and the following: Cell Wall: The cell wall is made of cellulose and is there to strengthen and support the cell. Chloroplasts: Are found in the green parts of plants. They are green because they contain chlorophyll. Chlorophyll absorbs light energy to make food by photosynthesis. Vacuole: The vacuole is a large space within the plant cell’s cytoplasm, filled with sap. It is important for keeping the cell, and thus the plant, rigid. Diagram cited from: http://misstutor.com/biology/lesson-­‐1-­‐%E2%80%93-­‐plant-­‐and-­‐
animal-­‐cell-­‐2/ III. Bacterial Cells
Bacteria are single cellular microorganisms consisting of a cytoplasm; a cell membrane and they are surrounded by a cell wall. The genetic material floats freely within the cell, as they don’t contain a nucleus. Some will be surrounded by a slime capsule and some may have a long protein strand attached to it in the form of a tail; a flagella. The bacteria use the flagella to move around. Some bacteria cause disease, whilst others are very useful to us. We use them in the production of cheese and yoghurt and we also contain many good bacteria in our stomachs. Diagram cited from: http://pixshark.com/real-­‐bacterial-­‐cell.htm IV. Yeast Cells
Yeast is a single cellular microorganism that contains a nucleus with the genetic information, cytoplasm, cell membrane and is surrounded by a cell wall. Yeast cells are able to survive for a long time even when there is little oxygen available. When oxygen is available to yeast cells they can carry out aerobic respiration, using the oxygen to break down sugar and produce energy. When there is little oxygen available, yeast can carry out anaerobic respiration (fermentation). In this respect, we can use yeast for the production of bread and alcohol. Diagram cited from: http://www.bbc.co.uk/schools/gcsebitesize/science V. Specialised Cells
Cells may be specialized for a particular function. Their structure will be specific to the function they are carrying out. For example: VI. Fat Cells
Fat cells contain a small amount of cytoplasm and large amounts of fat and are able to expand 1000x their size in order to store excess fat that the body produces when more food is consumed than necessary. Fat cells contain few mitochondria, as the cell requires little energy. Diagram cited from: http://trynerdy.com/?p=1565 VII. Cone Cells from Human Eye
Cone cells are the light sensitive layer of your eye and are what allows us to see in colour. The outer segment contains visual pigment, which changes chemically in colored light. It requires energy to change it back to its original form. The middle segment is full of mitochondria (and contains the nucleus), which supply the energy required to form the pigment. This is what allows us to always see in colour. The final part contains the specialised synaptic terminal, which connects to the optic nerve. Diagram cited from: http://www.bio.miami.edu VIII. Root Hair Cells
Root hair cells are found close to the tips of growing roots. Plants need to take in a lot of water and dissolved mineral ions. The root hair increases the surface area for absorption and allows them to do this more efficiently. They are situated near the xylem tissue, which carries the water and mineral ions up the rest of the plant. They contain a large vacuole, which speeds up the movement of water from the soil to the root hair cell by osmosis. Diagram cited from: http://biology-­‐igcse.weebly.com/ IX. Sperm Cells
Sperm cells are generally released a long way from the egg they are going to fertilise. They carry the genetic information from the male parent and have to be able to travel the distance and then penetrate the egg to fertilise it. In order to enable them to do this they have the following adaptations: -­‐A long tail, which whips form side to side to enable movement. -­‐Many mitochondria in the mid section to provide the energy for the tail. -­‐Arcosome in the tip, with digestive enzymes to break down the outer layers of the egg. -­‐Large nucleus with the genetic information to be passed on. Diagram cited from: http://www.biology.lifeeasy.org/ X. Cell Size The typical size of a cell is very small: 20um (0.02mm) in width. As a cell grows, its surface area to volume ratio decreases and its requirement for more oxygen and food increases. Once the surface area is no longer big enough to absorb enough food and water for the cell, then it must divide or die. XI. Tissues and Organs Cells are the building blocks of life. A group of similar cells which all carry out the same job, are called a tissue. Your muscle tissue is all made up of identical muscle cells. An organ is a group of different tissues which all work together to do a particular job. Your heart is an organ and pumps blood around your body. Different organs work together as a part of an organ system. Your heart and blood vessels work together within your circulatory system. All of your organ systems together make up a living organism – you. Diagram cited by: http://kaylasmithhh.weebly.com/ QMC
1. What are the three structural differences between plant and animal cells? a) Chloroplasts, nucleus, cell wall b) Chloroplasts, nucleus, cell membrane c) Cell wall, chloroplasts, sap filled vacuole d) Chloroplasts, cell membrane, cell shape 2. Which of the following statements is true: a) As a cell’s size increases, its surface area to volume ratio increases. This means cell size has no limit. b) As a cell’s size increases, its surface area to volume ratio decreases. This means cell size has no limit. c) As a cell’s size increases, its surface area to volume ratio increases. This means cell size has no limited. d) As a cell’s size increases, its surface area to volume ratio increases. This means cell size is limited. 3. What is an organ? a) A group of cells working together in the same way b) A group of tissues working together c) Something that pumps blood around your body d) The digestive system 4. What does the cell membrane do? a) Controls what enters and exits the cell and keeps the cells shape b) Controls what the cell does c) Strengthens the cell d) Controls the chemical reactions that occur within the cell 5. What two properties does a sperm cell have? a) Long tail and pointed head b) Short tail and digestive enzymes in the head c) Large nucleus and short tail d) Long tail and digestive enzymes in the head 6. Which of the following statements is true? a) Fat cells contain a lot of mitochondria b) Fat cells have a large cytoplasm c) Fat cells can grow 1000x their original size d) Fat cells are unable to expand 7. What does a yeast cell contain? a) Cell wall, cell membrane, chloroplasts and nucleus b) Cell wall, cell membrane, nucleus and cytoplasm c) Cell wall, chloroplasts, nucleus and cytoplasm d) Cell membrane, nucleus, cytoplasm and chloroplasts 8. What do ribosomes do? a) They carry out the instructions for making new cells or organisms b) Control the passage of substances into and out of the cell c) Use oxygen to produce energy d) Make all the proteins needed in the cell 9. How is the genetic material found in a bacterial cell? a) In a nucleus b) Loose in the cell and as plasmids c) In the flagella d) The don’t carry any genetic information 10. What are the main structures within the root hair cell of a plant? a) Root hair, nucleus, cytoplasm, vacuole b) Root hair, chloroplasts, nucleus, cytoplasm c) Root hair, nucleus, mitochondria, chloroplasts d) Nucleus, root hair, vacuole, cytoplasm