Biology

• Nucleus


  Contains chromosomes made of DNA molecules
• Chromosome


  Carries a large number of genes
• Body cells


  Chromosomes are normally found in pairs
• Gene


  A section of a chromosome that provides instructions for the ribosomes to create proteins
• Humans have 46 chromosomes in every body cell, arranged in pairs
• One chromosome from each pair comes from our mother and the other from our father at fertilisation
• Zygote undergoes mitosis


  Makes many cells with exact copies of the 46 chromosomes
• Gametes


  Haploid, only have half the number of chromosomes to ensure the offspring is diploid
• Reasons cells go through the cell cycle

  • Growth and Development
  • Tissue Repair and Maintenance
  • Reproduction
• Mitosis


  A single cell divides into two identical daughter cells
• Stem cell


  An undifferentiated cell capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation
• Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells
• Stem cells from adult bone marrow can form many types of cells including blood cells
• Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant
• Treatment with stem cells may be able to help conditions such as diabetes and paralysis
• Therapeutic cloning


  An embryo is produced with the same genes as the patient, stem cells from the embryo are not rejected by the patient's body so they may be used for medical treatment
• The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections
• Cloning of rare species

  • To protect from extinction
• Cloning of crop plants with special features

  • To produce large numbers of identical plants for farmers
• Mitochondria are responsible for producing energy through aerobic respiration.
• The cytoplasm is where most chemical reactions take place, including protein synthesis.
• The nucleus contains the genetic material (DNA) that controls all cellular activities.
• Chloroplasts contain chlorophyll which absorbs light energy needed for photosynthesis.
• Vacuoles store water and waste products.
• Ribosomes synthesize proteins.
• Lysosomes break down unwanted materials inside cells.
• Where is DNA found in eukaryotic cells?

  Nucleus
• What is a chromosome?

  Structures in a cell that contain genetic material, also known as DNA
• What is the structure of DNA

  Double Helix
• Compare the number of chromosomes in human body cells and gametes.

  Humans have 46 chromosomes in every body cell and they are arranged in pairs. One

  chromosome from each pair comes from our mother and the other from our father at

  fertilisation. On the other hand, gametes only

  have half the number of chromosomes to ensure that the offspring is diploid (full DNA) rather

  than polyploid (too much DNA).
• What is a gene?


  A gene is a section of a chromosome. Genes are instructions for the ribosomes of the cell to

  create proteins. The proteins are responsible for many processes in our body and also for

  our characteristics.
• Why are chromosomes arranged in pairs?

  Chromosomes occur in pairs so that there won't be any possibilities of defective daughter cells that arise due to uneven distribution of chromosomes.
• How is the sex of a person determined?

  As the egg already holds an X chromosome, the sex of a person is determined by the next chromosome that it will receive from the sperm:

  If the egg receives another X chromosome from the sperm, the resulting individual is XX, meaning that ovaries are formed therefore the individual will be a female.

  If the egg receives another Y chromosome from the sperm, the resulting individual is XY, meaning that testes are formed therefore the individual will be a male.
• What are the 3 main stages of the cell cycle?

  -Interphase

  -mitosis

  -cytokinesis
• Diffusion


  The movement of particles from a high concentration to a low concentration
• Diffusion


  • Can only occur in liquids and gases because the particles can move around
  • Particles in solids only vibrate about a fixed position so cannot diffuse
• Diffusers


  • Perfumed oil diffusing from the reeds all around the room
  • High number of perfume molecules near the reeds
  • Lower number in the far corners of the room
• Perfume molecules diffuse


  From a high concentration to a low concentration
• In the body, gases such as oxygen and carbon dioxide diffuse into and out of cells
• Osmosis


  The diffusion of water through a partially permeable membrane