b2 cells and control

• There are 4 stages to mitosis : prophase, metaphase, anaphase, telophase (pmat)
• In prophase The DNA condenses to form chromosomes (become shorter and thicker) and The nuclear envelope starts to break down, leaving the chromosomes free in the cytoplasm.
• In metaphase The chromosomes line up at the equator (middle) of the cell. `
• In Anaphase Spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell. 
• In telophase the chromatids reach the opposite poles of the cell where they uncoil to become long and thin chromosomes again and A nuclear envelope forms around each set of chromosomes to form two nuclei.
• After the steps of mitosis, the cytoplasm divides in a process known as cytokinesis. This produces two daughter cells that are genetically identical to one another. 
• Nerve cells are adapted for transmitting messages from one part of the body, to another
• Explain how a sperm cell is adapted for its role?

  • has lots of mitochondria to provide energy for movement + is streamlined to make swimming easier
• two types of stem cells found in animals : embryonic stem cells and adult stem cells
• Two key features of stem cells:

  They can divide by mitosis to form more cells and differentiate into specialised cells.
• Adult stem cells can only differentiate into different types of blood cells
• What do we call the plant tissues that are continually growing and that contain stem cells?

  Meristems
• What is the problem in type 1 diabetes?

  Insulin deficiency due to damaged pancreas
• Paralysis is When nerve cells are damaged, messages can no longer be sent to the muscles properly leading to the loss of the ability to move some or all of your body.
• Steps of stem cell treatment - isolate stem cells from bone marrow, grow them in a lab, transplant them into the patient
• two drawbacks of using embryonic stems cells in stem cell therapy?

  • The embryonic stem cells must come from embryos. These are in limited supply, and some people have ethical objections to it, as they think the embryos could have developed into a person.
• Two risks of using stem cells in medicine?

  1. The stem cells could be infected with a virus whilst in the laboratory, which could then infect the patient.
  2. As stem cells divide quickly, there is a chance they could divide uncontrollably once they've been transplanted, and then develop into a tumour. 
• What passes along nerve cells?

  electrical impulses
• What is the gap between two neurones called?


  Synapse
• The CNS consists of the Brain and spinal cord
• A receptor detects a stimulus and sends a signal to the effector.
• What is the role of a sensory neurone?

  To transfer a signal from a receptor to the CNS
• What is the role of a motor neurone?


  To transfer a signal from the CNS to an effector
• What is the role of a relay neurone?

  To transfer a signal from a sensory neurone to a motor neurone
• What is a reflex?

  An automatic response to a stimulus
• pathway of Reflex Arc?

  stimulus ➔ receptor ➔ sensory neurone ➔ relay neurone ➔ motor neurone ➔ effector ➔ response