unit two: multicellular organisms

• chromosomes are made of DNA and are found in the nucleus
• human cells have 46 chromosomes - this is the chromosome complement
• In humans, all normal body cells contain 46 chromosomes. The 46 chromosomes are made up of 2 matching sets of chromosomes forming 23 pairs of chromosomes. in each pair, 1 chromosome came from mum and the other came from dad. Cells which have a double set of chromosomes, like human body cells, are known as DIPLOID
• There are 23 pairs of chromosomes in human cells (except sperm and egg cells)
• Each species has specific and characteristic number of chromosomes within each cell. This is known as the chromosome complement. Since chromosomes provide the genetic information for each species, it is essential that each new cell receives a full complement of chromosomes. This ensures that animals and plants are provided with all the characteristics of their species.
• During growth and repair, cells always divide by mitosis to maintain diploid chromosome number.
• Mitosis provides new cells for growth, repair of damaged tissues and replacement of dead or damaged cells. It also maintains the diploid chromosome complement.
• Diploid cells have two matching sets of chromosomes, which are replicated during mitosis.
• Cell division is an important process of a cell making two exact copies of itself
• The division of the nucleus during cell division is called mitosis
• Mitosis is important because…

  • it produces new cells for growth and repair of damaged cells

  • it maintains the diploid chromosome complement
• Inside nearly all cells is a nucleus. The nucleus contains instructions that control cell activities, including mitosis. The instructions are carried on chromosomes (composed of DNA)
• Mitosis is when one cell divides to form two daughter cells. Each daughter cell receives a complete set of chromosomes. To do this every chromosome in the parent cell must be copied before division can take place.
• All of the new cells produced must contain the same number of chromosomes as the original cell. This makes sure no genetic information is lost and every new cell can function correctly. They are genetically identical.
• All of the new cells produced must contain the same number of chromosomes as the original cell. This makes sure no genetic information is lost and every new cell can function correctly. They are genetically identical.
• step one of mitosis

  Nucleus contains long unfounded chromosomes. Each chrome doubles to form 2 identical chromatids

  
• step two of mitosis

  Chromosomes shorten and coil up. Nucleur embrace starts to disappear

  
• step three of mitosis

  chromatids line up the equator of the cell and spindle fibres attach to the centromere

  
• step four of mitosis

  pair of identical chromatids are pulled apart by spindle fibres to opposite ‘poles’ of the cell

  
• step five of mitosis

  new nucleur membranes form. cytoplasm divides

  
• step six of mitosis

  two daughter cells are formed each containing the diploid chromosome number. the daughter cells are identical to each other and the parent cell.

  
• stem cells are only found in animals and they are UNSPECIALISED. they have no specific function.
• stem cells can

  • undergo mitosis to self-renew

  • develop into specialised cells
• embryonic stem cells

  • found in very early embryos

  • they have the ability to develop into any type of cell the body requires

  • they can even develop into complete organs
• adult stem cells

  • these are sometimes called tissue stem cells and don’t have the same regenerative powers as embryonic stem cells

  • they are usually only regenerate cells associated with the tissues in which they are found
• Stem cells are involved in growth and repair
• tissue stem cells can be found in the body throughout life.
• examples of medical applications of stem cells

  • bone marrow transplant

  • skin grafts

  • repairing heart muscle

  • cornea repair
• Structure and function of a nerve cell

  Has connections at each end to link with other nerve cells. Can conduct electrical impulses.

  
• Structure and function of a red blood cell

  Has no nucleus so it can carry more oxygen. Contains haemoglobin. Is small and flexible to fit in capillaries

  
• Structure and function of sperm cell

  Has a tail to swim to the egg

  
• Structure and function of the root hair cell

  Has a large surface area to absorb more water. Has no chloroplasts as it is not exposed to light.

  
• Cell organisation hierarchy

  Cells -> tissues -> organs -> systems
• what feature of stem cells allows them to differentiate into many types of cell?


  Unspecialised
• Part of the brain - medulla


  Controls involuntary actions, heart rate, digestion and sleep
• cerebellum

  coordinates muscles, controls balance and posture
• cerebrum 


  thoughts and memories, senses and speech
• Neurons (nerve cells) carry information from the 5 senses to the central nervous system (CNS). The CNS can then process this information and react appropriately. This involves three types of neurons:

  • sensory neurons

  • inter neuron

  • motor neuron
• Sensory neurons

  transmit messages from sense receptor to the CNS
• Inter neuron

  transmit messages IN the CNS (specifically within the spinal cord)