Specialised Cells

• Cells are the basic building blocks of all living organisms
• As an organism develops , cells differentiate to form different types of cells - They become specialised
• If cells are specialised, they become more efficient at their job - but they may lose the ability to do other jobs
• Why do cells differentiate?

  To form different types of cells (To become specialised)
• Most types of animal cell differentiate at an early stage
• Many types of plant cell can differentiate throughout their life
• What is differentiation?

  When cells become specialised
• Most animal cells are specialised
• As a cell differentiates:

  • It may change shape  
  • It may develop adaptations or different sub-cellular structures to enable it to carry out a specific function 
• Sperm, nerve and muscle cells are all specialised animal cells
• The job of a sperm is to join with an ovum (egg cell) - This is called fertilisation
• During fertilisation , the genetic information of the sperm and ovum combine
• Explain how the nucleus and tail of a sperm have adapted:

  • Nucleus – this is where the genetic information is contained – However, sperm cells only contain half the genetic information of a normal adult cell  
  • Tail – Sperm cells have a long tail which propels them to swim to the ovum – they are also streamlined to make this easier  
• Explain why the sperm cell has adapted to have mitochondria and an acrosome:

  • Mitochondria – Sperm cells have many mitochondria, which are the major site of respiration – these give sperm cells the energy needed for swimming  
  • Acrosome – the sperm cell has an acrosome that contains enzymes to allow the sperm to penetrate/digest their way through the outer layer of the ovum 
• Fill in the labels for this diagram of a motor neurone

  A) Axon

  B) Sheath

  C) Cell body

  D) Dendrites

  E) Synapses
• The job of a nerve cell is to send electrical impulses around the body
• Describe the adaptations of a motor neurone:

  • Axon – The axon is long and carries the electrical impulses from one part of the body to the other  
  • Myelin / Sheath – Insulates the axon and speeds up the transmission of nerve impulses  
  • Synapses – Junctions which allow the impulse to travel from one nerve cell to another  
  • Dendrites – Increases the surface area so other nerve cells can connect more easily 
• Label the different parts of this motor neurone

  A) Axon

  B) Dendrites

  C) Cell Body

  D) Myelin / Sheath

  E) Synapses

  
• Muscle cells can contract
• Muscle cells work together to form muscle tissue
• True or false : Muscle cells have a nucleus?

  True
• Describe the adaptations of a muscle cell

  • Protein fibres – Change their length – When a muscle cell contracts, protein fibres shorten decreasing the length of the cell  
  • Mitochondria – Muscle cells have lots of mitochondria to provide energy for muscle contraction 
• Most plant cells are specialised
• Root hair , xylem and phloem cells are all specialised plant cells
• Describe the adaptations of a root hair cell

  • Root hair / Long projection – increase the surface area of the root, to absorb water and dissolved minerals more effectively  
  • No chloroplasts –Photosynthesis requires energy from light . Root hair cells cannot photosynthesize as they are underground, so do not need chloroplasts  
  • Mitochondria – Root hair cells have lots of mitochondria for the active transport of minerals 

  
• Xylem are found in the plant stem , and form long tubes - these tubes carry water and dissolved minerals from the roots to the leaves
• Describe the adaptations of Xylem cells?

  • Thick walls – xylem cells have thick walls containing lignin – this strengthens the cell wall and provides support to the plant  
  • End walls - Xylem cells are arranged end to end , but the end walls have completely broken down – this means that the cells can form a long hollow tube so water and dissolved minerals can flow easily 

  
• Because the cell walls are sealed with lignin , the xylem cells die
• Why do xylem cells have no nucleus , cytoplasm , vacuole or chloroplasts?

  This makes it easier for water and minerals to flow
• Phloem tubes carry dissolved sugars up and down the plant
• Describe the adaptations of a phloem cell?

  • Phloem cells have no nucleus and only limited cytoplasm , which allow dissolved sugars to move through the cell interior 
  • The end walls of phloem cells have pores (sieve plates), which allow dissolved sugars to move through the cell interior  
  • Phloem cells are arranged end to end in tubes  
  • Each phloem cell has a companion cell connected by pores 

  
• Because phloem vessel cells have very limited cytoplasm , they haven't got many mitochondria - so each phloem vessel cell has a companion cell connected by pores - Mitochondria in the companion cell provide energy to the phloem vessel cell