LGS A-Level OCR Biology - Unit 2 - Cell Organisation and Stem Cells
A cell is the basic structural, functional, and biological unit of all living organisms. It is the smallest unit of life that can carry out all essential life processes. Cells can exist as independent units of life (as in unicellular organisms) or as part of multicellular organisms.
Define cell
a single repeating unit of an organism
Key Terms
Define cell
a single repeating unit of an organism
Define tissue
a collection of differentiated cells that have a common function
Define organ
a group of tissues that work together to carry out a common function
Define organ system
a group of organs that carry out a common function
Define specialised
having particular structure to serve a particular function
Define differentiated
the process by which a less specialised cell develops a distinct form and function,a cell specialising
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| Term | Definition |
|---|---|
Define cell | a single repeating unit of an organism |
Define tissue | a collection of differentiated cells that have a common function |
Define organ | a group of tissues that work together to carry out a common function |
Define organ system | a group of organs that carry out a common function |
Define specialised | having particular structure to serve a particular function |
Define differentiated | the process by which a less specialised cell develops a distinct form and function,a cell specialising |
Why do multicellular organisms need specialised cells? | complex communication in a multicellular organism specialised functions need specialised cells maximise efficiency of processes like absorbing nutrients |
What features does an erythrocyte have to suit it for its function? | Biconcave disc- maximises SA to carry oxygen No nucleus- more room for haemoglobin Flexible- can squeeze through narrow capillaries |
What features does a neutrophil have to suit it for its function? | Multilobed nucleus- makes it easier for neutrphils to squeeze through small gaps Granular cytoplasm- contains many lysosomes which contain enzymes used to attack pathogens |
What features does a root hair cell have to suit its function? | Root hairs- increase surface area to maximise uptake of water/minerals from the soil |
What features does a sperm cell have to suit it for its function? | Mitochondria- supplies the energy to swim Tail- allows for movement Acrosome- contains digestive enzymes which digest protective layers around ovum |
What features does a palisade cell have to suit it for its function? | Chloroplasts- absorb a large amount of light Rectangular- packs closely to form a continuous layer Chloroplasts are able to move in cytoplasm- so can absorb more light |
What features does a guard cell have to suit it for its function? | Cell wall thicker on inside than outside- so cell doesn’t change symmetrically as its volume changes Gap in the centre- allows gases in and out |
What are the 4 main categories of tissues in animals? | Nerve tissue epithelial tissue muscle tissue connective tissue |
What are stem cells? | Undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of an organism |
Define undifferentiated | An unspecialised cell originating from mitosis or meiosis |
Define potency | the ability of a stem cell to differentiate into different cell types |
Define totipotent | A stem cell that can differentiate into any type of cell (including extra-embryonic) and form a whole organism |
Define pluripotent | a stem cell that can form all types of tissue but not a whole organism |
Define multipotent | can only form a range of cells from a certain cell lineage |
Give an example of where totipotent cells are found in a human | In a zygote |
Give an example of where pluripotent cells are found in a human | Blastocyst |
Give an example of where multipotent cells are found in a human | Blood stem cells |
What are the characteristics of stem cells? | can repeatedly undergo cell division not adapted to a specific function can give rise to specialist cells few epigenetic markers |
What are stem cells used for in the body? | growth development (of am embryo) tissue repair |
Where are stem cells found in plants? | Vascular cambium Meristematic tissue (e.g roots and shoots) |
How do cells become specialised? | all cells have the same DNA genes are switched on and off by epigenetics different proteins are produced in the cell so the cell can undergo a specialised function due to the proteins |
How long do erythrocytes live for? | 120 days |
How long do neutrophils live for? | 6 hours |