Biology - Cells Flashcards
What are the characteristics of a light microscope?
- Can magnify objects of up to 1000X
- Colour images
- 2D
- Ultrastructure of cells not shown
What are the characteristics of an electron microscope?
- Uses an electron beam instead of light
- Magnifying power up to 200 000X
- Reveals the ultrastructure of cells
- Colourless
- 3D
Define the term ‘magnification’.
Magnification refers to the number of times the image of an object is larger than the actual size.
What is the formula and unit for magnification?
Magnification = Image Size/Actual Size
The same unit has to be used for the size of image and size of specimen.
Size of image should be converted to micrometer (μm): 1mm = 1000μm
What is a cell and what does it consist of?
A cell is the building block of an organism. It consists of nucleic acids, proteins, carbohydrates and lipids.
What do all eukaryotic cells consist of?
All eukaryotic cells have a plasma membrane, cytoplasm, and nucleus.
Two major types of cells
Prokaryotes and Eukaryotes
What are the characteristics of a prokaryotic cell?
- Smaller than eukaryotic cells
- Simpler internal structure
- Lack membrane-bound organelles
- Bacteria are all prokaryotic cells
What is the structure of a bacterial cell?
- Single circular DNA as genetic material
- Has a cell wall, ribosomes, small circular DNA molecules (plasmids), flagellum
- Some are pathogenic (disease-causing)
What is the structure and characteristics of a virus (NOT A/MADE OF A CELL)?
- Protein coat and genetic material inside
- Living and non-living
- Does not grow, move, feed, respire or excrete
- Reproduces only in a host as the host contains enzymes and organelles like ribosomes for reproduction
Characteristics of eukaryotes
- Occur in organisms e.g. algae, fungi, plants, animals
- Generally much larger than prokaryotes
- Contain a distinct nucleus, cytoplasm and plasma membrane
- Compartmentalised internal cell structure and many membrane-bound organelles
What are the characteristics of a plasma membrane?
- Forms a physical boundary (separates) between the cytoplasm and the physical environment
- Selectively permeable
- The CELL MEMBRANE encloses some organelles in eukaryotes e.g. nucleus, mitochondria, Golgi apparatus
Define ‘selectively permeable’ and ‘partially permeable’.
Selectively permeable: Able to regulate the movement of substances according to the needs of the cell (e.g. plasma membrane)
Partially permeable: Only allows smaller molecules to pass through but excludes larger molecules. (e.g. Visking tubing)
What are the characteristics of a cell wall?
- Encloses the whole cell including plasma membrane
- Made of cellulose
- Protects cell and gives it a fixed shape
- Fully permeable
- Absent in animal cells
What are the characteristics of cytoplasm?
- In a eukaryotic cell, it is the site where most cellular reaction occurs
- An aqueous medium that contains dissolved substances and enzymes
- Contains many organelles
What are the characteristics of the nucleus?
- Surrounded by a double membrane called the nuclear membrane and nuclear envelope
- Contains genetic information (chromosomes/chromatin)
- Controls cell activities e.g. cell growth and repair of parts
- Essential for cell division
What is chromatin?
- Composed of mainly proteins and genetic material
- Contains all genetic information required for the survival of the cell
- When the cell is dividing, chromatin condenses into more tightly-coiled structures called chromosomes
What are the characteristics of the rough endoplasmic reticulum?
- Consists of a network of flattened spaces lined with a membrane
- Small particles called ribosomes are attached to its outer surface
- The outer surface of the RER is continuous with the nuclear membrane
- Transports proteins made by ribosomes to the Golgi body for secretion out of the cell
What are the characteristics of ribosomes?
- Small round structures that appear as dark granules in the cytoplasm of a cell
- Either attached to the membrane of the RER or lie freely in the cytoplasm
- Needed to synthesize proteins in the cell
- Attached to RER: Make proteins transported out of the cell
- In the cytoplasm: Make proteins used within the cytoplasm
- Have 1 small subunit and 1 large subunit
What are the characteristics of the smooth endoplasmic reticulum?
- No ribosomes attached to membrane and is more tubular than RER (connected to RER)
- Synthesizes substances such as fats and steroids (sex hormones)
- Converts harmful substances into harmless substances through detoxification
What are the characteristics of the Golgi body?
- Shaped like a disc, consists of a stack of flattened spaces surrounded by membranes
- Vesicles (tiny spherical spaces enclosed by a membrane) can be seen fusing with one side of the Golgi body and pinching off from the opposite side
- The Golgi body chemically modifies substances made by the ER
- stores and packages these substances in vesicles for secretion out of cell.
Process of substances secreted out of the cell by vesicles
- Small vesicles containing substances pinch off the ER
- Fuse with Golgi body; substances may be modified
- Secretory vesicles pinched off from Golgi body and move to plasma membrane
- Fuse with the plasma membrane and contents are released out of the cell
What are the characteristics of the mitochondria?
- The mitochondrion is bound by a double membrane
- Site of aerobic respiration where energy is produced in the form of Adenosine Triphosphate (ATP)
- The higher the energy requirement of the cell, the more mitochondria present
What are the characteristics of the chloroplasts?
- Oval structures found in plant cells
- Contain a green pigment called chlorophyll
- Large and double-membrane bound
What are the characteristics of the vacuoles?
- Fluid-filled space enclosed by a selectively permeable membrane called the tonoplast
- Vacuoles in plant cells contain cell sap; sugars, mineral salts, amino acids
- Vacuoles in animal cells are usually temporary and contain water and food substances
