Cell Specialisation

• • In order for a cell to become specialised, a process called Differentiation occurs, where unspecialised cells (called Stem Cells) produce cells with specialised structures.​
  • In plants, Stem Cells are found in Meristematic Tissue. New cells are continuously being produced since the plant continues to grow throughout its lifetime.​
  • In humans, early embryos consist of Stem Cells that can produce any type of cell. These cells are described as Totipotent.
• • Sperm Cells are specialised in a number of ways:​
  •  They have an Flagellum (tail) which allows it to move/swim towards the egg.​
  •  many mitochondria which generates energy propels the cell.​
  • The head of the cell contains an Acrosome, which is a specialised Lysosome that releases enzymes so that the Sperm Cell can penetrate the membrane of the Egg.​
  • Sperm Cells are also very small and thin/streamlined, which aids their movement.​
• They are the female gametes. They are haploid (they have half the mothers genetic information=23 chromosomes). It’s one of the largest cells in the human body at approximately 0.12mm in diameter. It contains:​

  •  a nucleus which houses the mother’s genetic information. ​
  • The zona pullucida is the outer protective membrane of the egg. ​
  • the corona radiata (follicular cells) which consists of two or three layers whose function is to supply proteins needed to the fertilised egg cell. 
• • Erythrocytes, commonly known as Red Blood Cells, carry oxygen from the lungs to respiring tissues. ​
  • There are specialised in several ways for their function:​
  • They contain large amounts of Haemoglobin, that holds oxygen, and many of the organelles (including the nucleus, ER & mitochondria) present in normal cells are not present in Erythrocytes, to make space for more Haemoglobin. ​

  ​

  • Their shape is biconcave, which maximises surface area, and so the speed of movement of Oxygen into and out of the cell.​
  • They are Small and flexible which allows them to squeeze through narrow capillaries.​
• Neutrophils are a type of White Blood Cell that ingests and destroys invading microorganisms. This process is called phagocytosis​
• ​white blood cells

  Features:

  • They have large amounts of Lysosomes, which contain enzymes that kill ingested cells. This makes their Cytoplasm appear Granular. ​
  • They also have a Lobed Nucleus, which allows for greater flexibility  so they can squeeze through small gaps when travelling to the site of infection. They engulf and digest pathogens (phagocytosis). ​
  • They have cell surface receptors to detect antigens from foreign pathogens. Once antigens are detected, white blood cell produce antibodies to counter the antigens and stop the bacteria from causing infection in the body. ​
• There are 2 types of lymphocyte – B cells and T cells​
• lymphocytes

  The B and T cells recognise foreign cells by proteins on their surface – antigens.​

  The T cells send chemical signals to the B cells.​

  B cells proliferate by mitosis and form Plasma cells produce antibodies.​

  Memory cells remain in the body to respond quickly if the pathogen is encountered again – this is how vaccines work.​
• label the nerve

  A) Dendrite

  B) Myelin sheath

  C) Node of Ranvier

  D) Axon

  E) Cell body (Neuron)

  F) Nucleus

  G) Schwann cell

  H) Axon terminal

  
• dendrite Conducts impulse towards the cell body​

  ​axon Conducts impulse away from the cell body​

  node of Ranvier Gaps between found between myelin sheath​

   axon terminal End of axons

  ​Cell body Contains the nucleus and is the metabolic centre of the cell
• • Muscles are composed of cells that are elongated and form fibres. ​
  • Muscle cells contain protein filaments called actin and myosin that enable muscles to contract and cause movement.​
• There are three types of muscle cell:​

  • Skeletal muscle cell (Voluntary/striated muscle)  is found attached to bones. You can control its contraction and relaxation, and it sometimes contracts in response to reflexes. ​
  •  Cardiac muscle cell is found only in the heart. It contracts at a steady rate to make the heartbeat. It is not under voluntary control. ​
  • Smooth muscle cell is found in the walls of hollow organs, such as the stomach and bladder. It is also not under voluntary control.​
• label

  A) skeletal muscle

  B) smooth muscle

  C) cardiac muscle

  
• • Because skeletal muscle cells are long and cylindrical, they are commonly referred to as muscle fibers.​
  • Skeletal muscle is composed of many muscle fibres​
  • Each muscle fibre is in turn composed of many myofibrils