A Level Biology a for OCR: Biology OCR A Flashcards

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How does a light microscope work?

Has 2 lenses (objective and eyepiece) Near the specimen Which the specimen is viewed through

The lens provides a magnified image

Which is magnified again by the eyepiece lens

Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed.


Magnification formula?


Magnification X Actual size of object


Animal cell

card image


Which organelles are included in an animal cell?

  • Nucleus
  • Nucleolus
  • Mitochondrion
  • Vesicles
  • Nuclear envelope
  • Golgi apparatus
  • Ribosomes
  • cell membrane
  • Smooth endoplasmic reticulum
  • Rough endoplasmic reticulum
  • lysosomes
  • cytoplasm
  • Centrioles
  • Microfilaments
  • Nuclear pores
  • Chromatin granules - DNA
  • Cytoskeleton

Microvilli - only appear in small intestine


What does the nucleus contain?

  • Coded genetic information in the form of DNA molecules
  • DNA directs the synthesis of all proteins required by the cell
  • The DNA and histone proteins are then put together to form chromatin which coils and condenses to make chromosomes



  • Area within the nucleus
  • produces ribosomes
  • Composed of proteins and RNA

RNA is used to produce ribosomal RNA (rRNA) which is then combined with proteins to form the ribosomes necessary for protein synthesis



  • The site of the final stages of cellular respiration
  • The energy is stored in the bonds of complex, organic molecules is made available for the cell to use by the production of ATP
  • The amount of mitochondria = amount of energy cell uses
  • Have a double membrane
  • Inner membrane is highly folded to form structures = Cristae
  • The fluid interior = the matrix
  • The membrane forming the cristae contains the enzymes used in aerobic respiration
  • They also contain small amount of DNA called mitochondrial (Mt)DNA
  • Can produce their own enzymes and reproduce themselves



  • Membranous sacs that have storage and transport roles
  • Single membrane
  • Used to transport materials inside the cell



  • Specialised forms of vesicles
  • Contain hydrolytic enzymes
  • Responsible for breaking down waste materials in cells (old organelles)
  • Play an important part in the immune system + apoptosis - programmed cell death



  • Present throughout the cytoplasm
  • network of fibres necessary for shape and stability
  • Organelles are held in place by the cytoskeleton and controls cell movement and the movement of organelles within the cell


3 components of the cytoskeleton


  • contractile fibres formed from actin
  • Responsible for cell movement and cell contraction during cytokinesis - when the cytoplasm of a single eukaryotic cell is divided to from 2 daughter cells


  • Globular tubulin proteins polymerise to form tubes that determine the shape of the cell
  • They also act as tracks for the movement of organelles around the cell
  • Spindle fibres (have a role in physical segregation of chromosomes in cell division) are composed of microtubules

Intermediate fibres:

  • These fibres give mechanical strength to cells and help maintain their integrity



  • Component of the cytoskeleton
  • Composed of microtubules
  • Two associated centrioles form the centrosome
  • Centrosome are involved in the assembly and organisation of the spindle fibres
  • In organisms with flagella and cilia, centrioles are thought to play a role in the positioning of them


Flagella and cilia

Flagella - whip-like

Cilia - Hair-like

  • They're extensions that protrude from some cells
  • Flagella are longer but cilia are found in greater amounts
  • Flagella are used to enable cells mobility
  • Used as sensory organelles in some cells - detecting chemical changes in the environment
  • Stationary cilia are present on the surface of the cell and have a function in sensory organs e.g. nose
  • Mobile cilia beat in a rhythmic manner, creating a current, and cause fluids or objects adjacent to the cell to move
  • E.g. present in the trachea to move mucus away from the lungs - helping to keep the air passage clean
  • Each cilium contains 2 central microtubules surrounded by 9 pairs of microtubules arranged like a wheel. Known as the 9+2 arrangement
  • Pairs of parallel microtubules slide over each other causing the cilia to move in a beating motion


Organelles of protein synthesis

Used for secretion - transport out of the cell

  • A significant proportion of the internal structure of a cell is required for this process
  • The ribosomes, the ER and the Golgi apparatus are linked and coordinate the production of proteins
  • The cytoskeleton plays a key role in coordinating protein synthesis


Endoplasmic reticulum

The ER is a network of membranes enclosing flattened sacs called cisternae

  • Connected to the outer membrane of the nucleus

Smooth endoplasmic reticulum:

  • Responsible for lipid and carbohydrate synthesis and storage

Rough endoplasmic reticulum:

  • Has ribosomes bound to the surface and is responsible for the synthesis and transport of proteins

Secretory cells, which release hormones or enzymes, have more rough ER than cells that don't release proteins



  • Can be free floating in the cytoplasm or attached to ER forming Rough ER
  • Not surrounded by membrane
  • they are constructed of RNA molecules made in the nucleolus of the cell
  • Mitochondria, prokaryotic cells and chloroplast also contain ribosomes


Golgi apparatus

  • Similar in structure to the Smooth ER
  • Compact structure formed of cisternae
  • Doesn't contain ribosomes
  • Have a role in modifying proteins and 'packaging' them into vesicles
  • May be secretory vesicles


How are Ionic bonds formed?

Give or receive electrons to form negative or positive ions that are held together by the attraction of opposite charges


How are covalent bonds formed?

Atoms share electrons unequally


What does polar mean?

unequal sharing of electrons when one is slightly positive or slightly negative (δ-) (δ+)


What is the electron share in water?

Oxygen has a larger share of electrons so its δ- whereas hydrogen is δ+


What is O-H bonded called?

Hydroxyl group


How do polar molecules interact with each other?

Polar molecules interact as the positive and negative regions of the molecule attract each other and form hydrogen bonds.


How does a light microscope work?

Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed.