All cells arise from other cells

• what is chromatid?

  one of the two copies of a chromosome that are joined together by a single centromere prior to cell division
• what is a chromosome?

  a thread-like structure made of protein and DNA by which hereditary information is physically passed from one generation to the next
• what is crossing over?

  the process whereby a chromatid breaks during meiosis and rejoins to the chromatid of its homologous chromosome so that their alleles are exchanged
• what is meiosis?

  the type of nuclear division in which the number of chromosomes is halved
• what is mitosis?

  a parent cell divides to produce two genetically identical daughter cells
• what are the two types of cell division in eukaryotic cells

  mitosis meiosis
• why is mitosis needed?

  growth and repair of damaged tissues in multicellular organisms
• what are the three main phases of the cell cycle?

  interphase mitosis cytokinesis
• what are the three phases within interphase?

  G1 (gap phase 1) S (synthesis) G2 (gas phase 2)
• what happens during G1 phase of interphase?

  cell grows and new organelles and proteins are made
• what happens during S phase of interphase?

  cell replicates its DNA ready to divide by mitosis
• what happens during G2 phase of interphase?

  cell keeps growing and proteins needed for cell division are made
• what are the four division stages of mitosis?

  prophase metaphase anaphase telophase
• describe interphase (3)

  cell carries out normal functions but prepares to divide cell's DNA unravelled and replicated to double genetic content organelles replicated and ATP content increased
• describe prophase (3)

  chromosomes condense to get shorter and fatter centrioles move to opposite ends of cell to form the spindle nuclear envelope breaks down and chromosomes lie free in cytoplasm
• what are centrioles?

  tiny bundles of proteins in a cell
• what is the spindle?

  network of protein fibres
• describe metaphase

  chromosomes line up along middle of cell and attach to spindle by their centromere
• describe anaphase (3)

  centromeres divide to separate each pair of sister chromatids spindles contract to pull chromatids to opposite poles of spindle, by the centromere chromatids appear v-shaped
• describe telophase (4)

  chromatids reach opposite poles of spindle and uncoil to become long and thin again (now chromosomes) nuclear envelope forms around each group of chromosomes to make two nuclei division of cytoplasm finishes mitosis finished and each daughter cells starts interphase for next round of mitosis
• describe cytokinesis (2)

  starts in anaphase, ends in telophase division of cytoplasm to form two daughter cells that are genetically identical
• give four factors that can affect the rate of cell division

  nutrients oxygen hormones genes
• what is cancer?

  uncontrolled division of cells that contain mutated genes
• what is a mutation?

  a change in the base sequence of DNA
• what mutagens can cause mutations of DNA? (2)

  ionising radiation from UV lights carcinogenic chemicals like in cigarette smoke
• how do cancer cells die?

  apoptosis destroyed by immune system which recognises them as 'foreign
• what is a tumour?

  where cancer cells keep on diving and layer on top of each other
• why are tumours dangerous? (3)

  damage organs they grow in cause blockages damage surrounding tissue
• what conditions do tumours exist in?

  need their own blood supply but often suffer from low oxygen as the blood supply cannot satisfy the tumour's oxygen demand due to high rate of cell division
• what are the two types of tumour?

  benign malignant
• describe a benign tumour (3)

  tumour grows slowly and is kept in one place do not invade other tissues or start tumours in other organs not usually life threatening
• describe a malignant tumour (3)

  tumour grows quickly invades other tissues and can break off and spread around the body likely life threatening
• what term describes a malignant tumour spreading around the body to cause tumours in other organs?

  metastasis
• how do cancer treatments help limit growth?

  controls the rate of cell division in tumour cells by disrupting the cell cycle, killing tumour cells and preventing further division
• what is the issue with cancer treatment?

  it cannot distinguish between tumour cells and normal cells, so they also kill normal dividing body cells (e.g hair cells, stem cells)
• what makes the cancer treatment worth it?

  tumour cells divide more frequently than normal cells so treatments are more likely to kill tumour cells
• give three examples of cancer treatments

  chemotherapy radiotherapy drugs
• describe chemotherapy (3)

  prevents synthesis of enzymes required for DNA replication stops cell cycle before S phase if DNA cannot replicate, cells cannot divide
• describe radiotherapy (3)

  damages DNA so cell will not pass S phase forces cell to kill itself by apoptosis cells will not divide and mitosis is prevented
• describe how drugs treat cancers (3)

  prevent spindle fibres from froming to stop mitosis stage one cell will contain double DNA and one will contain none prevents cell from functioning or dividing again