Biology

• The nucleus contains genetic information in the form of chromosomes. It controls cell activities such as cell growth and the repair of worn-out parts. It is essential for cell division, Cells without a nucleus, like the red blood cells of a mammal, are unable to divide.
• The cell membrane is made up of lipids and proteins. It is partially permeable membrane. Only allows some substances to pass through it and also controls the movement of substances in and out of the cell
• The cell wall is made of cellulose and protects the cell from injury and gives the plant cell a fixed shape. It is fully permeable, so it does not control what substances enter or leave the cell.
• Cytoplasm is a jelly-like substance that fills the inside of the cell and is enclosed by the cell membrane. It is where most cell activities occur.
• Organelles, such as mitochondria and ribosomes, are not visible under the light microscope. They can only be studied under an electron microscope.
• Vacuoles are partially permeable. Plant cells have large central vacuole which contains a liquid called cell sap. Cell sap contains sugars, mineral salts and amino acids. Animal cell have small vacuoles that contain water and food.
• Mitochondria are small oval or sausage-shaped organelles. Their function is to break down glucose in the presence of oxygen to release energy for cell activities. this process is called aerobic respiration.
• Ribosomes are small round structures. They are either attached to organelles within the cell or lie freely in the cytoplasm. They are needed to synthesise proteins in the cell.
• What does the ribosome do?

  the ribosome synthesise proteins in the cell.
• Chloroplasts are oval structures found in plant cells. They contain a green pigment called chlorophyll that is essential for photosynthesis.
• Red blood cells contain haemoglobin which binds to oxygen and transports it around the body. Has a circular, biconcave shape which increases the surface area-to-volume ratio so that oxygen can diffuse in and out at a higher rate. Lacks a nucleus, enabling the cell to store more haemoglobin for the transport of oxygen.
• Muscle cell is elongated and cylindrical in shape, contains many nuclei and mitochondria. Has mitochondria to provide energy for contraction of the muscle cell.
• Root hair cell has a long and narrow root hair to increase surface area-to-volume ratio to absorb water and mineral salts at higher rate.