Cells

• Active transport requires energy from ATP to move substances against their concentration gradients, while passive transport does not require energy as it moves substances down their concentration gradients.
• Simple diffusion of small and non-polar molecules down a concentration gradient
• Facilitated diffusion down a concentration gradient via protein carrier or channel
• Osmosis of water down a water potential gradient
• Active transport against a concentration gradient via protein carrier using ATP
• Co-transport of 2 different substances using a carrier protein
• Phagocytosis is a process in which white blood cells engulf pathogens thus destroying them

  They do this by fusing to a pathogen and enclose them in a phagocytic vacuole with a lysosome

  After the pathogen is engulfed and destroyed, its chemical markers called antigens are then presented on the surface of the phagocyte. The phagocyte then becomes an antigen presenting cell which activates an immune response if the antigen is recognised as foreign.
• Interphase – during this stage the cell grows and then prepares to divide – chromosomes and some organelles are replicated, chromosomes also begin to condense
• Cytokinesis – during cytokinesis the parent and replicated organelles move to opposite sides of the cell and the cytoplasm divides thus producing two daughter cells.
• Prophase

  • Chromosomes condense and are now visible when stained
  • The chromosomes consist of two identical chromatids called sister chromatids (each containing one DNA molecule) that are joined together at the centromere
  • The two centrosomes (replicated in the G2 phase just before prophase) move towards opposite poles (opposite ends of the nucleus)
  • Spindle fibres (protein microtubules) begin to emerge from the centrosomes (consists of two centrioles in animal cells)
  • The nuclear envelope (nuclear membrane) breaks down into small vesicles
• Metaphase

  • Centrosomes reach opposite poles
  • Spindle fibres (protein microtubules) continue to extend from centrosomes
  • Chromosomes line up at the equator of the spindle (also known as the metaphase plate) so they are equidistant to the two centrosome poles
  • Spindle fibres (protein microtubules) reach the chromosomes and attach to the centromeres
  • Each sister chromatid is attached to a spindle fibre originating from opposite poles
• Anaphase

  • The sister chromatids separate at the centromere (the centromere divides in two)
  • Spindle fibres (protein microtubules) begin to shorten
  • The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres (protein microtubules)
• Telophase

  • Chromosomes arrive at opposite poles and begin to decondense
  • Nuclear envelopes (nuclear membranes) begin to reform around each set of chromosomes
  • The spindle fibres break down
• • If a plant cell is placed in pure water or a dilute solution, water will enter the plant cell through its partially permeable cell surface membrane by osmosis, as the pure water or dilute solution has a higher water potential than the plant cell
• The cell surface membrane is primarily composed of a phospholipid bilayer. The tails of these phospholipids form a hydrophobic core, which acts as a barrier to most water-soluble substances
• Cholesterol molecules are present in the membrane, regulating its fluidity. They prevent the phospholipids from packing too closely together, thus maintaining the membrane’s stability at various temperatures
• Glycolipids and glycoproteins contain carbohydrate chains that exist on the surface of the membrane, enabling them to act as receptor molecules
• Proteins are embedded in the membrane, some of which function as transport proteins, creating hydrophilic channels that allow specific ions and polar molecules to pass through
• • The cell surface membrane regulates the movement of substances in and out of the cell, acting as a selective barrier
  • It helps maintain the shape of the cell, providing structure and support
  • It facilitates cell-to-cell communication through proteins involved in this process
  • It protects the cell by providing a barrier that shields the interior of the cell from damage
• Cell walls are made up of polysaccharides such as cellulose, chitin, peptidoglycan, and other materials depending on the type of organism.
• A cell wall surrounds many types of cells, including those found in plants and fungi.
• The main role of cell walls is to provide structural support and protection to the cell.
• In plants, cell walls consist mainly of cellulose fibers arranged in layers called microfibrils. These microfibrils give strength and rigidity to plant cells.
• Plant cell walls consist mainly of cellulose, while bacterial cell walls contain peptidoglycans.
• Animal cells do not have cell walls but instead rely on their plasma membranes for structural support.
• The primary functions of cell walls include protecting the cell against mechanical stresses, preventing excessive water loss or uptake, and supporting the cell's shape and rigidity.
• Certain viruses can infect animal cells by attaching themselves to specific receptors on the surface of the host cell's plasma membrane.
• Some bacteria may have no cell walls at all or only a thin layer of peptidoglycan.
• The nucleus is a membrane-bound organelle found in eukaryotic cells
• the nucleus contains the cell’s hereditary information in the form of chromatin, a complex of DNA and histone proteins
• The nucleus is separated from the cytoplasm by a double membrane known as the nuclear envelope
• The nuclear envelope has many nuclear pores that allow substances to enter and exit the nucleus
• Inside the nucleus, there is a dense structure called the nucleolus, which is made of RNA and proteins and is involved in ribosome assembly
• The nucleus contains the genetic material of the cell and controls the cell’s growth and reproduction, it plays a key role in gene expression and DNA replication (the process of making two identical copies of DNA in a cell)
• The nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (e.g., DNA polymerases) and signalling molecules to travel in
• • The Golgi apparatus is an organelle in eukaryotic organisms that is comprised of a series of flattened sacs, these sacs extend from the endoplasmic reticulum
• The Golgi apparatus moves molecules from the endoplasmic reticulum to their destination
• the Golgi apparatus modifies products of the endoplasmic reticulum to their final form
• The main function of the Golgi apparatus is to deliver vesicles, or packets of various cell products, to different locations throughout the cell
• The Golgi apparatus also tags vesicles with proteins and sugar molecules, which serve as identifiers for the vesicles so they can be delivered to the proper target