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| Question | Answer |
| All living things are made of cells. ~ Cells can be prokaryotic or eukaryotic. ~ Eukaryotic cells are complex and include all animal and plant cells. ~ Prokaryotic cells are smaller and simpler. ~ Eukaryotes are organisms made up of eukaryotic cells. ~ A prokaryote is a single-celled organism. | The different parts of a cell are called subcellular structures. Most animal cells have the following subcellular structures: |
| Nucleus - contains genetic material that controls the activities of the cell Cytoplasm - gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions. Cell Membrane - holds the cell together | and controls what goes in and out. Mitochondria - these are where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work. Ribosomes - these are where proteins are made in the cell. |
| Plant cells usually have all the bits that animal cells have, plus a few extra: Rigid cell wall - made of cellulose. It supports the cell and strengthens it. Permanent Vacuole - contains cell sap, a weak solution of sugar and salts. | Chloroplasts - these are where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll, which absorbs the light they need for photosynthesis. |
| Bacterial cells are much smaller. Bacteria are prokaryotes. They don't have chloroplasts or mitochondria or a true nucleus. Instead, they have a singular circular strand of DNA that floats freely in the cytoplasm. It has a cell membrane and wall. They may also contain one or more small rings of DNA called plasmids. | |
| Prokaryotic cells (like bacteria) can reproduce using a type of simple cell division called binary fission. It is virtually the same as mitosis but with the organelles that make up the prokaryotic cell. | Bacteria can divide quickly given the right conditions (e.g. a warm environment and lots of nutrients). Some bacteria, such as E. coli, can take as little as 20 minutes to replicate in the right environment. However, if conditions become unfavourable, the cells will stop dividing and eventually begin to die. |
| Cells differentiate to become specialised. Differentiation is the process by which a cell changes to become specialised for its job. As cells change, they develop different subcellular structures and turn into different types of cells. This allows them to carry out specific functions. Most differentiation occurs as an | organism develops. In most animal cells, the ability to differentiate is then lost at an early stage, after they become specialised. However, lots of plants cells don't every lose this ability. The cells that differentiate in mature animals are mainly used for repairing and replacing cells, such as skin or blood cells. |
| Identifying Specialised Cells: | |
| Sperm cells are specialised for reproduction: The function of a sperm cell is to get the male DNA to the female DNA. It has a long tail and a streamlined head to help it swim to the egg. There are lots of mitochondria to give it energy. It also carries enzymes in its head to help it digest through the egg cell membrane. | Muscle cells are specialised for contraction: The function of the muscle cell is to contract quickly. The cells are long (so they have space to contract) and contain lots of mitochondria to generate the energy needed for contraction. |
| Nerve cells are specialised for rapid signalling: The function of the nerve cell is to carry electrical signals from one part of the body to another. The cells are long (to cover more distance) and have branched connections at their ends to connect with other nerve cells and form a network throughout the body. | Root hair cells are specialised for absorbing water and minerals: Root hair cells are on the surface of a plant's roots, which grow into long 'hairs' that stick out into the soil. This gives the plant a big surface area for absorbing water and mineral ions from the soil. |
| Phloem and Xylem cells are specialised for transporting substances: Phloem and Xylem cells form phloem and xylem tubes, which transport substances such as food and water around plants. To form tubes, the cells are long and joined end to end. | Xylem cells are hollow in the center and phloem cells have very few subcellular structures, so that stuff can flow through them. (Subcellular - something that adds on to the cell to make it specialised) |
| What happens when a cell becomes specialised? They become specialised through cell differentiation. This is the process where a cell changes to become specialised for a certain job. As they change, they develop different subcellular structures, and turn into different types of cells. | Why is it important that cells specialise / differentiate? It is important that cells differentiate because they help to replace and repair damaged cells, such as skin or blood cells. If we didn't have specialised cells our bodies would not be able to function, eg: we would not have any organs. |
| __Chromosomes__ Most cells in the body have a nucleus. This contains genetic material in the form of chromosomes. These are coiled up lengths of DNA molecules. Each chromosome carries a large number of genes. Different genes control the development of different characteristics, eg: hair colour. | In a human body cell you can find 23 pairs of chromosomes. Body cells normally have two copies of each chromosome - one from the organism's 'mother' and one from its 'father'. So humans have two copies of chromosome 1, two copies of chromosome two... etc. |
| __The process of Mitosis__ | Body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle. The stage when the cell divides is called mitosis. Multicellular organisms use mitosis to grow or replace cells that have been damaged. The product is two daughter cells identical to the mother cell |
| In an undivided cell, the DNA is spread out in long strings. The cell has to grow and and increase the amount of subcellular structures (such as mitochondria and ribosomes) Then it duplicates its DNA (one copy for each new cell) The copied DNA forms x-shaped chromosomes. Each 'arm' is an exact duplicate of the other | The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite end of the cell. Then membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells - the nucleus has divided. Lastly, the cytoplasm and the cell membrane divide. |
| __Stem Cells__ Animals: Stem cells are found in early human embryos and bone marrow. Embryonic stem cells can differentiate to become any type of cell. Adult stem cells can only change into certain cells, such as blood cells. | Plants: Stem cells are found in the meristems (part of the plant where growth occurs). Throughout the plants entire life the stem cells can change into any type of plant cell. These can be used to make clones of whole plants quickly and cheaply, and can be used by farmers to grow crops that have specific features. |
| __Stem Cell Ethics__ Pros of Adult: Doesn't kill donor. -/- Permission can be given. -/- Tried and tested method. Cons of Adult: Painful procedure to remove. -/- Fewer diseases can be treated. -/- Risk of operation. | Pros of Embryonic: Better to use an embryo rather than waste it. -/- Treats a wide range of diseases (pluripotent). -/- Painless procedure. Cons of Embryonic: They cant give consent. -/- Harm or death of an embryo. -/- Long term effects are unknown. |
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