Biology paper 1

• What is a cell?


  A cell is the smallest unit of life that can replicate independently.
• What is the difference between prokaryotic and eukaryotic cells?

  Eukaryotic cells are larger and more complex, and include all animal and plant cells. On the other hand, prokaryotic cells are smaller and simpler (generally unicellular organisms) and do not have nuclei, such as bacteria.
• What organelles are found in plant cells and animal cells?


  The organelles that are found in both animal and plant cells are the cell membrane, nucleus, ribosomes, mitochondria, and cytoplasm.

  
• What organelles do plant cells have that animal cells don't?


  Plant cells have a permanent vacuole, chloroplasts, and a cell wall, whereas animal cells do not.

  
• What is the function of the cell membrane?


  The function of the cell membrane is to control what enters and leaves the cell. It can do this because it is selectively permeable.
• What is the function of the nucleus?


  The nucleus stores DNA, and so controls most of the cell's processes.
• What are the function of mitochondria?

  The function of mitochondria is to produce ATP (energy) via aerobic respiration.
• What are the function of ribosomes?

  The function of ribosomes is protein synthesis.
• What is the function of cytoplasm?


  Cytoplasm is the site of chemical reactions (gel-like substance, made from water, sugars, and salts).
• What is the function of the permanent vacuole?


  The permanent vacuole is filled with cell sap (a weak solution of sugars, amino acids and salts) to help keep the cell turgid.
• What are the function of chloroplasts?


  Chloroplasts are the site of photosynthesis, and contain chlorophyll, which is a green pigment that absorbs the light needed for photosynthesis. This process makes food for the plant in the form of glucose.
• What is the function of the cell wall?


  The cell wall is made from cellulose, and therefore strengthens the cell and keeps it from bursting if too much water is in the cell due to osmosis.
• What is the average size of an animal cell?

  The average size of an animal cell is between 0-30 micrometers.
• What is the average size of a bacterial cell?

  The average size of a bacterial cell is 1 micrometer.
• What is the average size of a virus?

  The average size of an animal cell is between 10-100nm.
• What organelles do bacterial cells not have?

  Bacterial cells do not have chloroplasts, mitochondria or a nucleus.

  
• Where is the DNA stored in bacteria?


  In bacteria, DNA is stored in the nucleoid (long strand of DNA that contains important genes) and plasmids (small circular strands of DNA that contain extra, useful genes e.g. antibiotic resistance). The plasmids can be transferred via the pilli to other bacteria.
• What are the advantages and disadvantages of light microscopes?

  The advantages of light microscopes are that they are cheap and easy to use. However, since they depend on light, they have a lower resolution than electron microscopes due to the longer wavelength of light.

  
• What can be seen using a light microscope?


  Light microscopes can be used to see individual cells and large subcellular structures, such as nuclei.
• What are the advantages and disadvantages of electron microscopes?

  The disadvantages of electron microscopes are that they are expensive and difficult to use. However, they have a higher resolution since they depend on electrons (wave-particle duality principle), which have a shorter wavelength than light.
• When was the electron microscope first used?

  The electron microscope was first used in 1933.
• What can be seen using an electron microscope?


  Electron microscopes can be used to see much smaller things in more detail, such as the internal structure of mitochondria and chloroplasts. They can also be used to see smaller things, such as ribosomes and plasmids.
• What is the formula for calculating magnification?

  magnification = image size/actual size
• How would you use a light microscope to look at onion cells?


  1) To use a light microscope to look at onion cells, you should first prepare the slide: add a drop of water, the epidermal tissue of the onion with tweezers, and iodine solution for colour and clarity. You should then cover the slide with the cover slip carefully to prevent air bubbles, which can obstruct the view of the specimen.

  2) You should then attach the slide to the stage.

  3) You should then use the course adjustment knob to bring the lowest-powered objective lens to roughly above the slide.

  4) If necessary, you should then turn on the light source.

  5) You should then use the fine adjustment knob to increase the definition of the image.

  6) If necessary, you should repeat this process with higher magnification objective lenses.

  7) Finally, you should draw your observations, using a sharp pencil and using at least half the space available without colouring/shading. You should label the organelles with clear, uncrossed lines, and include a title and scale.

  
• What is cell differentiation?

  Cell differentiation is the process by which cells become specialised.
• What are undifferentiated cells called?

  Undifferentiated cells are called stem cells.
• What is the purpose of sperm cells?

  The purpose of sperm cells is reproduction.
• How are sperm cells specialised for reproduction?


  Sperm cells are specialised for reproduction by their long tail, streamlined head to help them swim to the egg, by containing lots of mitochondria to provide the energy needed for this process, and by carrying enzymes to digest through the egg cell membrane in the acrosome (tip of the head). Sperm cells also only have 23 chromosomes.

  
• What is another term for nerve cells?


  Another term for nerve cells is neurons.
• What is the function of nerve cells?


  The function of nerve cells is rapid signalling: to carry electrical signals from one part of the body to another.
• How are nerve cells specialised for rapid signalling?

  Nerve cells are specialised for rapid signalling because they have a long axon to allow the electrical signals to travel more distance, and are branched at their ends (have dendrites) to connect to other nerve cells and form a network. They also have a myelin sheath which surrounds the axon to prevent electrical nerve signals leaking out of the nerve cell, which increases the speed of transmission of electrical signals.

  
• What is the function of muscle cells?


  The function of muscle cells is to be able to contract (shorten) to allow movement of body parts.
• How are muscle cells specialised for contraction?


  Muscle cells are specialised for contraction by being long, so that the protein fibres have space to contract, and containing lots of mitochondria to generate the energy needed for contraction.

  
• What is the function of root hair cells?

  The function of root hair cells is to absorb water and mineral ions from the soil.
• How are root hair cells specialised for absorbing water and mineral ions?


  Root hair cells are specialised for absorbing water and mineral ions by having a large surface area due to their long projections into the soil, and by containing lots of mitochondria to fuel the necessary process of active transport.

  
• What is the function of phloem cells?


  The function of phloem cells is to transport the products of photosynthesis (glucose) from the leaves to the rest of the plant.
• How are phloem cells specialised for transporting substances?


  Phloem cells are specialised for transporting substances by having very few subcellular structures, so that glucose and other food molecules can flow (in both directions).

  
• What is the function of xylem cells?

  The function of xylem cells is to transport water and mineral ions up the plant from the roots to the shoots.
• How are xylem cells specialised for transporting substances?


  Xylem cells are specialised for transporting substances by being hollow (dead cells joined end to end to form a tube that is strengthened by lignin).

  
• What is a micrometer in standard form?


  In standard form, a micrometer is 1x10^-6m.