Biology paper 1

• Cell


  The basic unit of life
• Microscope


  • Used to see cells and other tiny specimens
  • Light microscopes can magnify up to 2000 times
  • Electron microscopes can magnify up to 2 million times
• Using a microscope


  1. Adjust the objective lens

  2. Focus the specimen on the stage

  3. View the specimen through the eyepiece
• Units of measurement


  • Kilometre (km)
  • Metre (m)
  • Centimetre (cm)
  • Millimetre (mm)
  • Micrometre (μm)
  • Nanometre (nm)
• 1 μm = 1000 nm
• First light microscopes developed

  Mid-17th century
• Light microscopes use a beam of light to form an image
• Electron microscopes use a beam of electrons to form an image
• Transmission electron microscope


  • Gives 2D images with very high magnification and resolution
• Scanning electron microscope


  • Gives dramatic 3D images but lower magnifications
• Electron microscopes are large, very expensive, and have to be kept in special temperature, pressure, and humidity-controlled rooms
• Calculating magnification with a light microscope


  Multiply the magnification of the eyepiece lens by the magnification of the objective lens
• When labelling drawings made using a microscope, the magnification given should be the magnification at which the specimen was viewed
• Calculating the size of an object

  1. Know or can measure two of the factors

  2. Find the third
• Magnification triangle formula


  size of image / magnification = size of real object
• The cell has a diameter of 25 μm
• Magnifying power


  The ability of a microscope to make things look bigger
• Resolving power


  The ability of a microscope to distinguish between two separate points
• Light microscope has a resolving power of about 200 nm
• Scanning electron microscope has a resolving power of about 10 nm
• Transmission electron microscope has a resolving power of about 0.2 nm
• The cells that make up your body are typical animal cells
• Animal cells


  • Have a nucleus that controls all the activities of the cell
  • Have a cell membrane that controls the passage of substances into and out of the cell
  • Have mitochondria where aerobic respiration takes place
  • Have ribosomes where protein synthesis takes place
• Plant cells


  • Have a cell wall made of cellulose that strengthens the cell and gives it support
  • Have chloroplasts that contain chlorophyll and allow the plant to photosynthesise
  • Have a permanent vacuole filled with cell sap that helps keep the cell rigid
• Eukaryotic cells


  Have a cell membrane, cytoplasm, and genetic material enclosed in a nucleus
• Prokaryotic cells


  Have cytoplasm and a cell membrane surrounded by a cell wall, but the genetic material is not enclosed in a nucleus
• Bacteria are examples of prokaryotes
• Bacteria may have a protective slime capsule, flagella to move around, and plasmids that code for specific features
• Some bacteria are harmful and can cause diseases or decompose and destroy stored food
• Many bacteria have little or no effect on other organisms and are very useful
• Orders of magnitude


  Used to make approximate comparisons between numbers or objects, where each order of magnitude is about 10 times bigger
• As an organism develops, cells differentiate to form different types of specialised cells
• Relative sizes of different cells and whole organisms

  • e
  • dif
  • ba
  • 100m-
  • giant redwood
  • 10m
  • minke whale
  • 1m
  • human
  • συ
  • er
  • human eye 10cm-
  • apple
  • e2
  • 1 cm -
  • wasp
  • 1mm
  • ant
  • 100 μπ
  • light
  • microscope
  • eukaryotic cells
  • 10μm-
  • prokaryotic cells
  • 1 με
  • S
  • electron
  • microscope
  • 100 nm
  • 10 nm
  • PLOT
  • viruses
  • DNA
  • 1 nm
  • a small molecule
• Although the smallest living organisms are only single cells, they can carry out all of the functions of life. Most organisms are bigger and are made up of lots of cells. Some of these cells become specialised to carry out particular jobs.
• As an organism develops, cells differentiate to form different types of specialised cells. Most types of animal cells differentiate at an early stage of development, whereas many types of plant cells retain the ability to differentiate throughout life. As a cell differentiates, it gets different sub-cellular structures that enable it to carry out a particular function. It has become a specialised cell
• Some specialised cells, such as egg and sperm cells, work individually. Others are adapted to work as part of a Tissue, an organ, or a whole organism
• Nerve cells


  • They are specialised to carry electrical impulses around the body of an animal
  • They have several adaptations including lots of dendrites to make connections to other nerve cells, an axon that carries the nerve impulse from one place to another, and nerve endings or synapses that are adapted to pass the impulses to another cell or between a nerve cell and a muscle in the body using special transmitter chemicals
  • They contain lots of mitochondria to provide the energy needed to make the transmitter chemicals
• Muscle cells


  • They are specialised cells that can contract and relax
  • Striated muscle cells have three main adaptations: they contain special proteins that slide over each other making the fibres contract, they contain many mitochondria to transfer the energy needed for the chemical reactions that take place as the cells contract and relax, and they can store glycogen, a chemical that can be broken down and used in cellular respiration by the mitochondria to transfer the energy needed for the fibres to contract
• Sperm cells


  • They have a long tail that whips from side to side to help move the sperm through water or the female reproductive system, the middle section is full of mitochondria which transfer the energy needed for the tail to work, the acrosome stores digestive enzymes for breaking down the outer layers of the egg, and a large nucleus contains the genetic information to be passed on
• Root hair cells


  • They greatly increase the surface area available for water to move into the cell, they have a large permanent vacuole that speeds up the movement of water by osmosis from the soil across the root hair cell, and they have many mitochondria that transfer the energy needed for the active transport of mineral ions into the root hair cells