Cell structure and organisation Flashcards
(28 cards)
What can light microscopes show you?
objects magnified to 1000x and images are coloured
What can electron microscopes show you?
Images magnified to more than 200000x and images are black and white
What is a cell?
It is a unit of life. It consists of mass of living matter called protoplasm
What is protoplasm made of?
It is made up of three parts : the cell membrane, cytoplasm, nucleus
What is the function of the cell surface membrane?
controls the movement of substances in and out of the cell
Characteristics of cell membrane
- It is partially permeable
- It is made of lipid molecules, protein groups and carbohydrate groups
What are the functions of cell wall?
- It serves as a protection against injury for the plant cells
- It gives plant cells a fixed shape
- It prevents the plant cells from bursting when too much water enters them
Characteristics of cell wall
- It is made of cellulose
- It is fully permeable to all substances
Which organelles are not able to be seen under the light microscope and only electron microscope?
Mitochondria, endoplasmic reticulum, golgi apparatus and ribosomes
What are the functions of a nucleus?
+ nuclear membrane
- It controls cell activities such as cell growth and repair of worn-out parts
- It is essential for cell division
- It also contains chromatin ( which consists of DNA and proteins)
- It makes mRNA which is used to make proteins that are responsible for traits
Nuclear membrane separates the contents of the nucleus from the rest of the cytoplasm
What is the function of the cytoplasm?
It is the site of where chemical reactions occur in a cell
Characteristics of Rough endoplasmic reticulum (RER)
- It is made up of a network of flattened spaces lined with membranes which are continuous with the nucleus membrane.
- Surface appears rough due to ribosomes attached to its surface
Functions of RER
It transports proteins made by attached ribosomes to the Golgi apparatus for secretion out of the cell.
Function of ribosomes
attached to RER & free lying in the cytoplasm
- (attached to RER) make proteins that are usually transported out of the cell
- (lying freely in cytoplasm) make proteins that are used within the cytoplasm of that cell
- main function is synthesising proteins
Functions of smooth endolasmic reticulum (SER)
- Synthesises substances such as fats and steroids (sex hormones in mammals are steroids)
- converts harmful substances to harmless substances - detoxification
Characteristics of SER
- more tubular than RER
- does not have ribosomes attached to its membrane
Functions of golgi apparatus
- chemically modifies substances made by the endoplasmic reticulum
- stores & packages these substances in vesicles for secretion out of the cell
How are substances synthesised secreted out of the cell?
- (in the context of protein) proteins are synthesised by ribosomes on the rough endoplasmic reticulum
- Small vesicles containing proteins/ substances made by the ER are then pinched off the RER (for proteins) / ER (for substances made by the ER)
- These small vesicles fuse with Golgi apparatus, releasing their contents into the Golgi apparatus. The Golgi apparatus carries out chemical modifications to these proteins/ substances.
- Secretory vesicles containing the modified proteins/ modified substances then pinches off from Golgi apparatus.
- These secretory vesicles move towards the cell surface membrane and fuse with the cell surface membrane and release its contents out of the cell
Function of mitochondria
It is the site of aerobic respiration where food substances (glucose) are broken down to release energy to be used by the cell to perform cell activities such as growth and repair
Function of chloroplasts
It contains a green pigment called chlorophyl which is essential for plants to photosynthesise and make food
Vacuoles in animals & plants
Vacuoles are fluid-filled spaces enclosed by a partially permeable membrane which stores substances within the cell.
Animal cells:
- numerous small vacuoles, contain water and food substances
- exist temporarily
Plant cells :
- large central vacuole, stores cell sap which contains dissolved substances like sugars, mineral salts and amino acids
Differences between plant and animal cells
- Plant cells have cellulose cell walls which are absent in animal cells
- Plant cells contain chloroplasts which are absent in animal cells
- Plant cells contain a large central vacuole while animal cells have small vacuoles
Define differentiation (in terms of specialised cells)
The process by which a cell becomes specialised for a specific function
Specialised cells : RBC
Adaptations of RBC
- Contains haemoglobin - which binds reversly to oxygen, so oxygen can be transported from lungs to all parts of the body
- Has circular and biconcave - increases SA:V ratio for faster rate of diffusion of oyxgen in and out of the RBC
- Lacks nucleus - enables RBC to pack more haemoglobin to bind reversely to more oxygen for faster tranportation of oxygen around the body
- Flexible and elastic - enables RBC to be able to change into a bell shape to squeeze through narrow blood capillaries so RBC are in close proximity to body cells, reducing diffusion distance, allowing faster rate of diffusion of oxygen to cells