biology

• The two types of cells are:

  1. Prokaryotic
  2. Eukaryotic
• Animal and plant cells are eukaryotic. They have a

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Bacterial cells are prokaryotic and are much smaller. They have a:

  • cell wall
  • cell membrane
  • cytoplasm
  • single circular strand of DNA (small rings of DNA found in the cytoplasm)
• Cells are extremely small, and we can use orders of magnitude to understand how much smaller or bigger one is than the other.
• In animal and plant cells they have a:

  • nucleus (contains DNA coding for particular protein needed to build new cells and is enclosed in a nuclear membrane.)
  • Cytoplasm (a liquid substance in which chemical reactions occur, contains enzymes and organelles)
  • Cell membrane (controls what enters and leaves the cell)
  • Mitochondria (where aerobic respiration reactions occur which provides energy for the cell)
  • Ribosomes (where protein synthesis occurs, found on a structure called the rough endoplasmic reticulum.)
• Plant cells only have (compared to animal cells):

  • Chloroplasts (where photosynthesis takes place, providing the food for the plant, contain chlorophyll pigment which harvests the light needed for photosynthesis.)
  • Permanent vacuole (contains cell sap, it's found within the cytoplasm and improves cell rigidity.)
  • Rigid cell wall (which is made of cellulose and provides strength to the cell.)
• Bacterial cells have:

  • Cytoplasm ( responsible for cell growth, metabolism, and elimination of waste and replication of the cell)
  • Cell membrane (forms a permeable barrier regulating the passage of solutes between the cell and environment.)
  • Cell wall (made of a different compound, peptidoglycan.)
  • Single circular strand of DNA ( as they have no nucleus, this floats in the cytoplasm)
  • Plasmids (small rings of DNA)
• Cells specialize by undergoing differentiation: a process that involves the cell gaining new sub-cellular structures for it to be suited for its role.
• Examples of specialised cells in animals:

  1. Sperm cells: to carry the male's DNA to the egg cell
  2. Nerve cells: to transmit electrical signals from one place in the body to another
  3. Muscle cells: to contract quickly to move the bones or simply squeeze
• Sperm cells have:

  • streamlined head and long tail to aid swimming
  • Many mitochondria which supply energy for the cell to move
  • The acrosome (top of the head) has digestive enzymes which break down the out layers of membrane of the egg cell
• Nerve cells are also known as neurons.
• Nerve cells have:

  • A long axon, enabling impulses to be carried long distances
  • having lots of extensions from the cell body means branched connections can form with other nerve cells
  • the nerve endings have many mitochondria which supply energy to make special transmitters chemicals called neurotransmitters.
• Muscle cells have:

  • special proteins (myosin and actin) that slide over each other causing the muscle to contract)
  • lots of mitochondria to provide energy from respiration for contraction
  • they can store a chemical called glycogen that is used in respiration by mitochondria
• Examples of specalised cells in plants:

  • Root hair cells ( to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots)
  • Xylem cells (to transport water and mineral ions up the plant from the roots to the shoots)
  • Phloem cells (to carry the products of photosynthesis to all parts of the plants)
• Cell differentiation is the system in which a stem cell changes from one type to a differentiation one.
• Magnification is the ability to make the image of a specimen seem larger than it actually is.
• Magnification = size of image/size of real object
• The resolution of a light microscope depends on wavelength of light used and the diameter of the lens. The shorter the wavelength of light, the higher the resolving power. A smaller lens has a greater resolving power.
• Resolution is a measure of a microscope's ability to distinguish between two points that are close together on an object.
• The nucleus contains your genetic information:

  • this is found in the form of chromosomes, which contains coils of DNA
  • A gene is a short section of DNA that codes for a protein and as a result controls a characteristic- each chromosome contains many genes
  • There are 23 pairs of chromosomes in each cell of the body, you inherit one from you mother and father, resulting in 46 chromosomes in total
  • Sex cells (gamete) are the exception, there are half the number of chromosomes, resulting in 23 chromosomes in each gamete cell
• The cell cycle:

  1. Interphase- The cell grows, organelles( such as ribosome and mitochondria) grow and increase in number , the synthesis of protein occurs, DNA is replicated and energy stores increase.
  2. Mitosis- The chromosomes line up at the equator of the cell and cell fibres pull each chromosomes of the 'X' to either side of the cell.
  3. Cytokinesis- Two identical daughter cells form when the cytoplasm and cell membranes divide.
• Cells at the early stage of development of the embryo are called stem cells.
• Types of stem cells:

  1. Embryonic stem cells
  2. Adult stem cells
  3. Meristems in plants
• Embryonic stem cells:

  • form when an egg and sperm cell fuse to form a zygote
  • they can differentiate into any type of cell in the body
  • can be used to replace insulin-producing cells for those suffering from diabetes
• Adult stem cells:

  • if found in bone marrow they can form many types of cells including blood cells.
• Meristems in plants:

  • found in the root and shoot tips
  • can differentiate into any type of plant for the rest of the plant's lifetime.
  • can be used to make clones of the plant
• Benefits of using stem cells for scientific reasons:

  1. Embryonic stem cells can replace insulin-producing cells for those suffering from diabetes.
  2. Embryonic stem cells can replace new neural cells for diseases such as Alzheimer's or nerve cells for those paralysed with spinal cord injuries.
  3. Adult stem cells can form many types of cells including blood cells.
  4. Meristem cells can clone plants which can save them from extinction.
• Cancer is caused by uncontrolled cell growth and division.
• The uncontrolled cell growth and division are a result of changes that occur to the cells and result in the formation of a tumour ( a mass of cells). Not all tumours are cancerous. They can either be benign or malignant.
• Benign is where the tumour grows until there is no more room. The tumour stays in one place (usually with a membrane) rather than invading other tissues in the body. This type isn't dangerous or cancerous.
• Malignant is where the tumour grows and spreads to the neighbouring healthy tissues. Cells can break off and spread to other parts of the body by travelling in the bloodstream. The malignant cells then invade healthy tissues elsewhere in the body and form secondary tumours. Malignant tumours are dangerous and can be fatal.
• Lifestyle risk factors for various types of cancer:

  1. Smoking - linked to lung, mouth, bowel, stomach and cervical cancer.
  2. Obesity - linked to bowel, liver and kidney cancer.
  3. UV exposure - linked to skin cancer.
  4. Viral infection - Hepatitis B and C.
• Diffusion is the movement of molecules from an area of high concentration of the molecules to an area with a lower concentration.
• Respiration is the process of transferring energy from glucose which goes on in every cell.
• Carbon dioxide = CO₂
• Aerobic respiration is respiration using oxygen and produces carbon dioxide and water.
• Equation for aerobic respiration:

  glucose + oxygen 🡢carbon dioxide + water

  C6H12O6 + 6O2 → 6CO2 + 6H2O
• Anaerobic respiration occurs without oxygen and releases less energy but more quickly than aerobic respiration.
• Word equation for anaerobic respiration:

   glucose → lactic acid
• Respiration fermentation is the process of breaking down glucose to release energy.