1.1 Introduction to cells Flashcards
What is cell theory
- Living organisms are composed of cells
- Cells are the smallest unit of life
- All cells come from pre-existing cells
All cells contain
- All living cells are surrounded by a cell membrane
- All cells contain genetic information which controls function of the cell
- Cells generate energy to power activities of the cell
Exceptions to cell theory
- Skeletal muscle fibre: atypical as they are 1000x longer than normal cells and have many nuclei
- Fungal Hyphae: sometimes are not divided up into many cells, this creates one larger cell (septate or aseptate)
- Giant Algae: these cells are abnormally large compared to other algae cells. 1 nucleus and they can be up to 100mm long.
Organisms consisting of once cell carry out all the functions of life - and other facts
- nothing smaller than a cell can survive
- subcellular substances/organelles can live independent of the cell
What does MR GREHN stand for?
Metabolism Response Growth Reproduction Excretion Homeostasis Nutrition
Metabolism as a function of life
produce enzymes to control chemical reactions inside cell, including respiration
Response as a function of life
perceiving and responding to changes in the environment (stimuli)
Growth as a function of life
increase in size and dry mass
Reproduction as a function of life
producing offspring - sexually/asexually
Excretion as a function of life
Expel waste matter
Homeostasis as a function of life
keeping conditions within the organisms within tolerable limits
Nutrition as a function of life
obtaining food to provide energy and materials for growth
Metabolism in paramecium and chlamydomonas
Paramecium: produces enzymes to catalyse reactions within the cytoplasm
Chlammydomonas: same
Response in paramecium and chlamydomonas
Paramecium: reacts to stimuli - reverses its direction of movement when it touches a solid object
Chlamydomonas: reacts to stimuli - senses the brightest spot (using eye spot) and swims towards it
Growth in paramecium and chlamydomonas
Paramecium: increase in size + dry mass by accumulating organic matter and minerals from its food
Chlamydomonas: increase in size + dry mass by photosynthesising and absorption of minerals
Reproduction in paramecium and chlamydomonas
Paramecium: reproduces asexually by mitosis or sexually by meiosis and gametes
Chlamydomonas: same
Excretion in paramecium and chlamydomonas
Paramecium: expels waste products of metabolism (e.g. CO2 diffuses out)
Chlamydomonas: expels waste products of metabolism (e.g. O2 diffuses out)
Homeostasis in paramecium and chlamydomonas
Paramecium: maintains all internal conditions within limits (e.g. expels water using contractile vacuole)
Chlamydomonas: same
Nutrition in paramecium and chlamydomonas
Paramecium: Feeds on smaller organisms by ingesting and digesting them in vesicles (endocytosis)
Chlamydomonas: Produces its own food by photosynthesis using chloroplasts which take up much of the cell
SA : Vol ratio is important in the limitation of cell size
- In the cytoplasm of a cell many chemical reactions take place, these reactions are known as the metabolism of the cell.
- The rate at which chemical reactions can happen within a cell is proportionate to the volume of the cell.
- For metabolism to continue substances used in reactions must be absorbed by the cell and waste products removed.
- Substances move through the plasma membrane in and out of the cell.
- The rate at which substances can cross the membrane depend on its surface area.
Why a small SA : Vol ratio is bad
- If the surface area to volume ratio’ is too small then substances will not be able to enter the cell as quickly as they are required, and waste products will accumulate because they are produced more rapidly and can’t be excreted.
- If the surface to area ratio is too small then cells may overheat because metabolism produces heat faster that it is lost over the cells surface.
Multicellular organisms
- Many cells fused together to create a single mass of cells
- Cells are often specialised and together these cells create a functioning multicellular organism
- the cellular components of multicellular organisms are what allow them to function
Cell differentiation in multicellular organisms
- in multicellular organisms cells are specialised to perform different functions
- by becoming specialised, cells in a tissue can perform the function more efficiently than if they had many different roles
Gene expression and cell differentiation
- all cells in the human body have the same amount of genes however certain cells only express certain genes so that they can perform their function
- example of differentiation: skin cells inside the human nose all express different genes so that they can pickup different smells