B2

• 2.1: Describe mitosis as part of the cell cycle, including the stages

  interphase, prophase, metaphase, anaphase and telophase

  and cytokinesis


  Interphase: DNA Replication

  Prophase: DNA in chromosomes condense, becoming more visible. The nuclear membrane breaks down + dissapears and spindle fibres appear. Chromosomes move freely in the cytoplasm.

  Metaphase: The two chromatids line up on spindle fibres across the equator of the cell .

  Anaphase: The two chromatids separate and pulled apart on spindle fibres to opposite cell poles.

  Telophase: New membranes form around each full chromosome set at each pole of the cell -> two nuclei are formed with identical chromosomes. Spindle fibres disappear.

  
  

  Cytokinesis: the cell splits into two. Cell surface membranes/cell walls form to separate the identical cells.
• 2.1 - What happens in Prophase?

  DNA in chromosomes condense, becoming more visible. The nuclear membrane breaks down + dissapears and spindle fibres appear. Chromosomes move freely in the cytoplasm.
• 2.1- What happens in Metaphase?

  Metaphase: The two chromatids line up on spindle fibres across the equator of the cell .
• What happens in anaphase?

  The chromosomes are split, then the chromatids are pulled to either side of the cell by spindle fibres
• What happens in telophase?

  New membranes form around each full chromosome set at each pole of the cell -> two nuclei are formed with identical chromosomes. Spindle fibres disappear.
• What happens in cytokinesis?

  Divides cytoplasm to form two identical daughter cells
• 2.2 Describe the importance of mitosis in growth, repair and asexual reproduction

  Mitosis is important in growth + repair as it produces identical cells.

  
  

  Mitosis is important in asexual reproduction as there's only one parent. It produces CLONES, whose cells are IDENTICAL to the parent. It is faster + doesn't need others.
• 2.3: Describe the division of a cell by mitosis as the production of

  _ _ cells, each with _ _ of chromosomes in_ _ to the _ _, and that this results in the formation of two _ _, __body cells

  Mitosis produces 2 DAUGHTER CELLS.

  These cells have identical sets of chromosomes in the nucleus to the parent cell.

  Mitosis results in the formation of 2 GENETICALLY IDENTICAL body cells.
• 2.4: Describe cancer as the result of _ in _ that lead to _ _ _


  Cancer is a result of CHANGES in CELLS

  This leads to UNCONTROLLED CELL DIVISION
• 2.5: Describe growth in organisms, including:

  a cell division and differentiation in animals

  b cell division, elongation and differentiation in plants


  Growth happens by cell division (mitosis) and growth often happens when young until full growth.

  In younger animals, cell division is at a faster rate -> more growth.

  In mature animals, cell division is mostly used for repair not growth.

  Cells divided by mitosis eventually DIFFERENTIATE to become different types of SPECIALISED cell.

  
  

  Most cells stop differentiating at early stages - specialised cells with nuclei divide by mitosis.
• 2.5: Describe growth in organisms, including:

  b cell division, elongation and differentiation in plants


  Growth happens firstly in the MERISTEM at the end of shoots/roots due to rapid cell division

  Growth occurs due to cell elongation (zone of elongation) due to intake in water (osmosis) in vacuoles.

  Cells also differentiate into specialised cells which have particular functions (zone of differentiation): xylem/phloem, root hair cells.
• 2.6: Explain the importance of cell differentiation in the

  development of specialised cells

  Differentiation produces specialised cells, adapted/specialised to carrying out specific functions.

  They make up a whole multi-cellular organism + specialised cells make them work more effectively
• 2.7: Demonstrate an understanding of the use of percentiles charts

  to monitor growth


  Percentile charts measurements (head circumference/length/mass) are divided into 100 groups. We find the percentage of readings BELOW a PERCENTILE.

  If the Xth percentile for an N month old baby's mass is Y kg. X% of N month old babies will have a mass BELOW Y kg.

  CURVED LINES show the RATE OF GROWTH of a baby at the SAME PERCENTILE.

  Measuring mass regularly + plotting it helps identify if babies are growing normally. Babies should remain NEAR THE SAME PERCENTILE CURVE (varying a small amount)

  CONCERNS: over 95th percentile, below 5th (not growing properly) and baby size increases by more than 3 lines.
• 2.8: Describe the function of embryonic stem cells, stem cells in

  animals and meristems in plants

  EMBRYONIC STEM CELLS are cells taken from embryos at early stages of division

  They can divide to produce any type of specialised animal cell.

  (When embryos develop areas - limit to types of specialised cell)

  Can replace/repair damaged: brain cells (treat Parkinson's); retina cells (treat blindness). Used to grow transplants/drug testing tissue.
• 2.8: Describe the function of stem cells in

  animals

  ADULT STEM CELLS are taken from differentiated tissue in an animal (e.g. bone marrow)

  As the animal is fully developed, stem cells lose ability to produce other specialised cells - only produced surrounding tissue stem cells

  Can treat leukaemia (bone marrow cancer) + potentially new tissues genetically matched to patients
• 2.8: Describe the function of meristems in plants


  PLANT MERISTEM CELLS are taken from rapidly growing parts: root/shoot meristems

  Can divide and differentiate to produce any type of specialised plant cell for as long as the plant lives.

  Can be used to clone rare plants to stop their extinction

  Can produce cloned crop plants for farmers with desirable traits.
• 2.9: Discuss the potential benefits and risks associated with the

  use of stem cells in medicine - all

  ALL STEM CELLS

  Benefits: Replace faulty, diseased cells with healthy, specialised ones and stimulate their growth - scientific interest for cures if disease.

  Drawbacks: REJECTION (the immune system can kill cells put in) of cells from another person. CANCER (stem cells don't stop dividing after replacing damaged ones)

  Viruses inside cells can infect cells + if not spotted, could spread.
• 2.9: Discuss the potential benefits and risks associated with the

  use of stem cells in medicine- embryonic stem cells

  EMBRYONIC STEM CELLS

  Benefits: Easy to extract from embryos + produces any cell type.

  Drawbacks: Embryos destroyed when cells are removed - some believe in right to life (ethical issue). Some believe curing patients is important.
• 2.9: Discuss the potential benefits and risks associated with the

  use of stem cells in medicine- adult stem cells


  ADULT STEM CELLS

  Benefits: No embryo destroyed (no ethical/religious issue)

  Already used to treat disease by bone marrow transplants which can differentiate into specialised cells

  Drawbacks: Produce a narrow range of cell types + only from the tissue around them.
• 2.13: Explain the structure and function of sensory neurones

  SENSORY NEURONES: Carry impulses from receptor cells to the CNS. Dendrite branches collect impulses from receptor cells. Impulses passed into them are transmitted along a long dendron to the cell body in the middle of the neurone. A short axon transmits impulses away from the cell body to the series of axon terminals, passing impulses to other neurones.
• 2.13 Explain the structure and function of motor meurones

  MOTOR NEURONES: Carry impulses from the CNS to effectors. Dendrite branches receive impulses from other/relay neurones and they pass nerve impulses to the cell body. The impulse is transmitted along a long axon from the cell body to a series of axon terminals, passing impulses to effector cells. (No dendrons).
• 2.13: Explain the structure and function of relay neurones


  RELAY NEURONES: Carry impulses from between neurones and makes up the tissue of the CNS. Dendrite branches pass nerve impulses from the sensory neurone to the cell body. The axon transmits impulses away from the cell body to axon terminals, passing impulses to other neurones. This can link sensory + motor neurones
• 2.13: Explain the structure and function of myelin sheath.

  FATTY MYELIN SHEATHS surround long dendrons +/ axons. They electrically insulate neurones from neighbouring ones in nerves to stop signals losing energy. They make impulses "jump" along cells between gaps in the myelin, speeding up neurotransmission.
• 1.13: Explain the structure and function of synapses in the transmission of electrical impulses


  SYNAPSES: The connection between 2 neurones - a small gap. When nerve impulses reach axon terminals at the ends of a neurone/axon, the impulse causes a neurotransmitter chemical to be released (from vesicles) into the gap and diffuse across it. The chemical fits into receptors and this generates a new impulse in the next neurone.
• 1.13: Explain the role of neurotransmitters

  NEUROTRANSMITTERS slow down neurotransmission BUT are only released from ONE axon terminal to ensure impulses only flow one way (ONLY RECEPTORS on the other neurone). They let fresh impulses be generated in neurones connected to one neurone so the original impulse doesn't split
• 2.14: Explain the structure and function of a reflex arc including

  sensory, relay and motor neurones.


  A reflex arc: neurone pathway) from receptor to effector bypassing parts of the brain used to process information.

  When a stimulus is detected by receptor cells, an impulse is created.

  The impulse is transmitted in along a sensory neurone.

  Released neurotransmitters diffuse across the gap and generate an impulse in the relay neurone and it is transmitted along it.

  The impulses are transmitted along the motor neurone's axon to the effector.

  This brings about a rapid response (e.g. muscle contraction)