B1

• Cells are the basic unit of all living organisms
• Cells that have a nucleus, such as plant and animal cells, are called eukaryotic cells 
• Cells without a nucleus, such as bacteria, are called prokaryotic cells.
• what cell is this?

  animal cell

  
• Nucleus : holds all the genetic material (including DNA) needed to control the cell’s activities.  
• Cytoplasm : jelly-like substance that contains nutrients, salts and enzymes required for chemical reactions to take place.
• A semi-permeable cell membrane : controls what comes in and out of the cell. 
• mitochondria : contain enzymes needed for respiration, which releases energy for the cell to use. 
• Ribosomes : production of proteins.
• what cell is this?

  plant cell

  
• cell wall : made of cellulose that provides structure and protection to the cell. 
• Vacuole : holds weak solution of sugar and salts called cell sap that keeps the cell swollen
•  Chloroplasts : site of photosynthesis in the cell. 
• chlorophyll : a green pigment that absorbs the light and specific enzymes required for photosynthesis to occur and food to be produced.  
• what cell is this

  bacterium/bacteria cell

  
• Bacteria cells do not have a nucleus (prokaryotic), their genetic material is free in the cytoplasm. They have a main circular strand of DNA and occasionally additional small rings of DNA called plasmids. 
• Differentiation is the process by which different types of cells develop their specific set of cell structures and become specialised
• Stem cells are undifferentiated cells which means they have the ability to develop into different types of cells.
• Sperm cell


  • Sperm cells are specifically designed for the effective transport of male DNA to the female DNA for sexual reproduction.
  • The head of the sperm contains all the genetic information ready for fertilisation and has enzymes that are able to digest the egg cell membrane.
  • They also have lots of mitochondria to provide the energy required for movement and a tail to help it swim. 

  
• Nerve Cells


  • Nerve cells are specialised for rapidly carrying electrical impulses around the body.
  • They have a long axon to carry the impulse over long distances and are branched at both ends so they can connect and pass signals between one another
  • They are also insulated in a fatty sheath which helps the impulse move along the nerve quickly.

  
• Muscle cell


  • Muscle cells must be able to contract quickly so they contain lots of mitochondria to provide energy for the contraction and have protein filaments that slide over to cause the muscle to contract.

  
• root hair cells


  Root hair cells in plants are an exchange surface, specialised for absorbing water and nutrients from the soil.

  They are found on the plant’s roots and increase the surface area for efficient absorption.

  They also have a vacuole full of cell sap that is more concentrated than soil water which creates a water potential gradient for efficient water absorption.

  They also have lots of mitochondria to provide energy for the active transport of mineral ions from the soil.
• • Xylem cells form the xylem vessel which transports water and dissolved ions in a plant.
  • The cells of the xylem are dead and hollow and do not have top and bottom cell walls, subcellular structures or cytoplasm.
  • This allows water to be drawn upwards.

  
• phloem


  • Phloem cells form the phloem which is responsible for the transport of sugars and amino acids around the plant.
  • Cells are joined end to end with sieve plates between them to allow the passage of substances. 
• light microscopes


  Light microscopes use light and lenses to create a magnified image of a specimen. Their development enabled scientists to view individual cells and their larger subcellular structures such as nuclei.
• electron microscopes


  Electron microscopes have much  greater  magnification  and  resolving  power  because they use electron beams instead of light which have a much smaller wavelength. The development of the electron microscope allowed scientists to see cells in much more detail including the internal structures of mitochondria, chloroplasts and nuclei, and tiny structures like ribosomes and plasmids.
• ‘Resolution’ or ‘Resolving power’ is the ability to distinguish between two points.
• magnification formula

  
• Microscopy


  The use of microscopes
• How light microscopes work

  1. Light from the room hits the mirror

  2. Reflected upwards through the object

  3. Passes through the objective lens

  4. Passes through the eyepiece lens

  5. Into the eye
• Object


  The real object or sample that you're looking at
• Image


  The image that we see when we look down the microscope
• Magnification


  How many times larger the image is than the object
• Magnification = image size / object size
• Resolution


  The shortest distance between two points on an object that can still be distinguished as two separate entities
• Higher resolution means more detail and less blurriness
• Parts of a light microscope

  • Base
  • Arm
  • Light source (lamp or mirror)
  • Stage
  • Objective lenses
  • Eyepiece lens
  • Body tube
  • Coarse and fine focusing knobs
• Eukaryotic cells divide in a process called mitosis
• cell cycle : the series of events that occur in a cell to produce a new cell

  
• Mitosis produces 2 daughter cells that are identical to the original cell with the same number of chromosomes.