Introduction to cells Flashcards
Outline the cell theory
- All living organisms are composed of cells
- Cells are the smallest unit of life
- All cells come form pre-existing cells
Exceptions to the cell theory
- Striated muscle fibre:
- muscle cells fuse to form very long fibres (>300 mm)
- hundreds of nuclei despite a single continuous plasma membrane
- idea challenged: cells always function as independent units - Giant Algae
- unicellular, one nucleus, very large (can reach 100mm)
- idea challenged: large organisms are always made of many microscopic cells - Aseptate fungi (hyphae)
- hyphae - filamentous structures making up fungi
- some fungi not separated by septa (internal wall) –> continuous cytoplasm
- idea challenged: living structures are composed of discrete cells
Functions of life
- Nutrition - obtaining food, to provide energy and the materials needed for growth
- Metabolism - chemical reactions inside the cell
- Growth - an irreversible increase in size
- Response - the ability to react to changes in the environment
- Excretion - getting rid of the waste products of metabolism
- Homeostasis - maintaining stable internal conditions
- Reproduction - producing offspring either sexually or asexually
Unicellular organisms carry out all the functions of life in that cell
Outline the activities occurring in the volume and SA of a cell.
- The rate of metabolism (large number of chemical reactions) depends on the volume (cytoplasm) of the cell.
Requires absorption of nutrients and removal of waste (produced by reaction) - The rate of material exchange depends the SA (plasma membrane) of the cell.
Passage of substances - nutrients and gases enter, waste materials leave.
Relationship between cell size and SA:V ratio
As the size of the cell increases the SA:V ratio decreases. This is because the volume increases at a faster rate than SA.
Explain why cells are limited in size by SA:V ratio
As a cell grown bigger its volume will increase, metabolic rate increases, and SA (rate at which substances can move) will decrease steadily. Eventually the SA will be unable to accommodate the requirements of the volume (metabolism). The cell has to divide, or it will die.
If the SA:V ratio is small the cells may overheat because metabolism produces heat faster than it is lost.
Adaptions of cells that maximise SA:V ration
- Villi (of intestine) - ruffled structure, increases SA of inner lining of intestine
- Microvilli (on alveoli of lungs) - membranous extensions, increases SA
- other long extensions such as neurons
- thin flat shapes
Emergent properties in multicellular organisms
- Multicellular organisms are capable of completing functions that unicellular can’t due to the interactions and collective work. of its individual cells.
- Emergent properties are characteristics that arise from the interaction of individual component parts:
1. Cells may be grouped together to form tissues (epithelium)
2. Organs are formed from functional grouping of multiple tissues (stomach)
3. Organs that interact may form organ systems capable of carrying out specific body function (digestive system)
4. Organ systems collectively carry out the life functions of the complete organism
Define tissue
A specialised group of cells that perform the same function
Define differentiation
The development of specialised structure and functions in a cell as it matures.
Outline the benefits of differentiation in a multicellular organism
By becoming specialised, the cells in a tissue can carry out their function more effectively than if they had many different roles. (More efficient than unicellular organism)
They can develop the ideal structure, with the enzymes needed (to carry out chemical reactions).
220 specialised cell types in humans due to differentiation.
Example of specialised cells
- Red blood cells, carry oxygen. Transported when muscle cells contract.
- Rod cell in retina of the eye, absorb light and transmit impulses to brain
Describe the relationship between cell differentiation and gene expression
All cells share an identical genome - each cell contains the entire set of genetic instruction for that organism. The activation of different genes (given by chemical signals) is used to make proteins or other gene products. Cell differentiation takes place different genes are expressed in different cell types.
Defnie zygote and embryo
Zygote - cell resulting when a sperm fertilizes an egg cell.
Embryo - an organism in early stages of development after the zygote divides
List 2 key properties of stem cells that have made them active areas of research in biology and medicine today
- Self renewal: they can continuously divide, producing large quantities of new cells (useful for the growth of tissues or replacement of cells).
- Potency: (stem cells are not fully differentiated) they can differentiate into specialised cell types.
