Diversity in animals

• single-celled organisms are small and have a large surface area to volume ratio (SA/V) so oxygen can diffuse across plasma membrane and waste products can diffuse out via the same membrane
• Differentiation #1

  • multicellular eukaryotic organisms starts off as a single undifferentiated cell , called a zygote
  • this is when an ovum (egg cell) is fertilised by a spermatozoon and the two haploid nuclei fuse to give a diploid nucleus
  • zygote isn't specialised and all the genes in its genome are able to be expressed and divided by mitosis
  • after several mitiotic divisions, an embryo forms, containing many undifferentiated embryonic stem cells
• Differentiation #2

  • these embryonic cells differentiate as genes are switched off and other genes may be expressed more so that :

  - the proportions of the different organelles differs from those of other cells

  - the shape of the cell changes

  - some of the contents of cell changes

  this means each cell type is specialised for a particular function
• Erythrocytes and Neutrophils 1

  • erythrocytes carry oxygen from lungs to respiring cells
  • neutrophils ingest invading pathogens
  • they both derive from stem cells in bone marrow
• Erythrocytes

  • small , around 7.5µm in diameter, have large SA:V so oxygen can diffuse into cell membranes and easily get in all regions of cell
  • flexible, they have a well developped cytoskeleton which allows them to change shape so they can twist + turn when in narrower capillaries
  • this gives more space for haemoglobins; they are synthesised during differentiation using nucleus, mitochondria , ER, ribosomes and cytoplasm
• Neutrophils

  • they are about as twice the size of erythrocytes, and each neutrophil contains a nultilobed nucleus
  • they are attracted to and travel towards infection sites by chemotaxis
  • their function is to ingest bacteria and some fungi by phagocytosis
• Spermatozoa

  • the many mitochondria carry out aerobic respiration. AtP provides energy for undulipodium movement
  • because spermatozoa are small but long and thhin, they can move easily
  • once the spermatozoon reaches an ovum, enzymes are released from the acrosome (spcialised lysosome). They digest outer protective covering of the ovum, allowing the sperm head to enter the ovum
  • the head of the sperm contains the haploid male gamete nucleus and very little cytoplasm
• Epithelial Cells

  • lining tissue that's found on the outside of your body and on the inside
  • squamous epithelial cells are flattened in shape
  • Many of the cells in epithelium have cilia