A2.2 Cell Structure Flashcards
What is a cell?
Cells are the basic structural units of living organisms.
What does cell theory state?
Cell theory states that:
All living organisms are made up of one or more cells
Cells are the smallest units of life and are the basic functional unit in living organisms
New cells are produced from pre-existing cells
Why are stains used in microscopy when making temporary mounts?
Stains are used when making temporary mounts to provide colour contrast for cellular structures that might otherwise be transparent; this means that the structures can be seen under a microscope.
How is a coverslip used during preparation of a temporary mount of cells?
When making a temporary mount of cells a coverslip is gently lowered over a specimen after liquid and/or stain has been added.
Describe how a slide can be viewed using a light microscope.
A slide can be viewed using a light microscope as follows:
place slide onto microscope stage
lower the low power objective lens towards the stage as far as possible
use the coarse focus to locate the specimen
use the fine focus to bring the specimen into clear view
change the objective lens to increase magnification
repeat steps 3-5 as necessary
What is an eyepiece graticule?
An eyepiece graticule is a transparent scale mounted within the eyepiece lens of a light microscope.
How can an eyepiece graticule be used to determine the size of a specimen?
An eyepiece graticule can be used to determine the size of a specimen by calibrating the graticule using a stage micrometer. This process allows the actual length of each eyepiece graticule unit to be determined, and the eyepiece graticule can be used like a ruler to measure the length of a specimen.
What is the formula for calculating the actual size of a specimen?
The formula for calculating the actual size of a specimen is:
actual size = image size ÷ magnification
What is the formula for calculating magnification?
The formula for calculating magnification is:
magnification = image size ÷ actual size
Describe how a scale bar can be added to a biological drawing of a specimen viewed using a light microscope.
A scale bar can be added to a biological drawing as follows:
calibrate the eyepiece graticule and use it to measure the length of the specimen
calculate 20 % of the length of the specimen (or a similar percentage)
draw the specimen according to the rules of biological drawing
use a ruler to draw a line that is 20 % of the length of the drawing
write the actual length represented by the scale bar next to the bar; this should be a whole number
How do electron microscopes generate images?
Electron microscopes generate images by passing a beam of electrons through a specimen (TEM) or by bouncing electrons off the surface of a specimen (SEM).
What are the advantages of electron microscopes over light microscopes?
Advantages of electron microscopes over light microscopes are that they:
have higher resolving power
can magnify objects many more times (x500 000 compared to x2000)
can be used to show the details of internal cellular structures
How are specimens prepared using freeze fracture techniques?
Specimens can be prepared using freeze fracture methods as follows:
a specimen is rapidly frozen
the frozen tissue is broken apart, or fractured, exposing a surface that can be viewed
For what purpose is cryogenic electron microscopy used?
Cryogenic electron microscope is used for viewing the 3D structures of, e.g.:
proteins
viruses
cell membranes
How can fluorescent stains be used in microscopy?
Fluorescent stains are used in light microscopy; the dyes bind to specific target structures inside cells and then emit light when irradiated, showing where the structures are located within the cell.
What is immunofluorescence in microscopy?
Immunofluorescence uses antibodies with fluorescent dyes attached; the antibodies bind to specific target molecules and the dyes fluoresce when irradiated, showing whether or not, or where, the target molecules are present.
Which molecule makes up the genetic material of typical cells?
The genetic material of typical cells is made from DNA.
What is the role of DNA inside cells?
The role of DNA inside cells is to store the information needed to make proteins.
What is the role of cytoplasm within cells?
The role of cytoplasm within cells is to provide a medium in which the chemical reactions of cell metabolism can occur.
Why is it important that cells are surrounded by a plasma membrane?
It is important that cells are surrounded by a plasma membrane because it:
separates cells from their surroundings
allows cells to control which substances enter and leave
allow cells to communicate with other cells
What is a prokaryotic cell?
A prokaryotic cell is a type of cell that is small, unicellular and contains no internal membranes.
What are the components of a prokaryotic cell?
Components of a prokaryotic cell include:
cell wall
plasma membrane
cytoplasm
naked DNA in a loop
70S ribosomes
There are other structures found in some prokaryotes.
What is the role of a prokaryotic cell wall?
The role of a cell wall in prokaryotes is to maintain cell shape and prevent the cell from bursting due to water intake by osmosis.
How do prokaryotic ribosomes compare with eukaryotic ribosomes?
Prokaryotic ribosomes (70S) are smaller than eukaryotic ribosomes (80S).
What are two examples of gram-positive eubacteria?
Two examples of gram-positive eubacteria are:
Bacillus
Staphylococcus
What are the features common to eukaryotic cells?
The features common to eukaryotic cells include:
plasma membrane
compartmentalised cytoplasm
80S ribosomes
nucleus
mitochondria
endoplasmic reticulum
Golgi apparatus
vesicles, including lysosomes
cytoskeleton
What is the plasma membrane?
The plasma membrane is a partially permeable bilayer of phospholipids that surrounds all cells and controls the exchange of materials between the internal and external environment.
Define the term compartmentalisation in the context of cells.
Compartmentalisation refers to the separation of the cell interior into compartments, e.g. the mitochondrial matrix is separated from the rest of the cytoplasm.
Describe the composition of eukaryotic chromosomes.
Eukaryotic chromosomes are made of DNA bound to histone proteins.
What is the function of the Golgi apparatus?
The function of the Golgi apparatus is to modify molecules, e.g. proteins, before packaging them into vesicles for transport to their destination.
What is the function of the endoplasmic reticulum?
The function of the endoplasmic reticulum is as follows:
rough endoplasmic reticulum:
protein synthesis
protein transport
smooth endoplasmic reticulum:
lipid synthesis
production of sex hormones
calcium ion storage in muscle cells
What are lysosomes?
Lysosomes are a type of vesicle containing hydrolytic enzymes. They are involved with breaking down:
old organelles
pathogens during phagocytosis
biological molecules stored inside cellular vacuoles
What are microtubules?
Microtubules are hollow fibres made of tubulin protein that form part of the cell’s cytoskeleton, providing support and enabling movement of substances around the cell.
What are the process of life that occur in unicellular organisms?
Process of life that occur in unicellular organisms are:
metabolism
reproduction
homeostasis
growth
response to stimuli
excretion
nutrition
movement
What is homeostasis?
Homeostasis is the maintenance of internal conditions within tolerable limits.
What is excretion?
Excretion is the disposal of metabolic waste products, including carbon dioxide from respiration.
Define the term metabolism.
A cell’s metabolism is all the enzyme-catalysed reactions occurring in a cell, including cell respiration.
What is the function of mitochondria in unicellular organisms?
The function of mitochondria in unicellular organisms is to release energy for cell processes through respiration.
How are cilia and flagella involved with the life processes of unicellular organisms?
Cilia and flagella are involved with movement and responsiveness. They allow unicellular organisms to move around in response to stimuli.
Which eukaryotic cell types have a cell wall?
Eukaryotic cell types with a cell wall are:
plant cells
fungal cells
How do the cell walls of plant cells and fungal cells differ?
The cell walls of plant and fungal cells differ in that plant cell walls are made of cellulose while fungal cell walls are made of chitin.
How does vacuole size and function vary between different eukaryotic cell types?
Vacuole size and function differs between different cell types as follows:
plant cells: large, permanent vacuoles used for carbohydrate storage and cell support
animal and fungal cells: small vacuoles with multiple functions, e.g. disposal of waste
Which eukaryotic cells contain chloroplasts?
Chloroplasts are found in plant cells.
What are aseptate hyphae?
Aseptate hyphae are strands of fungal cells with no cross-walls to separate the cells. This means that the hyphae contain continuous cytoplasm and multiple nuclei.
How are skeletal muscle cells atypical?
Skeletal muscle cells are atypical in that they:
are long
contain multiple nuclei
contain proteins that allow them to contract and relax
How are red blood cells atypical?
Red blood cells are atypical in that they:
contain haemoglobin
have no nucleus
have a biconcave disc shape
What are the conventions of biological drawing?
The conventions of biological drawing include:
Drawings should be on plain white paper
Lines should be clear, single lines with no sketching
No shading
The drawing should take up as much of the space as possible
The drawing should show visible structure with proper proportions
Label lines should be drawn with a ruler, should not have arrows and should not cross
Title and annotations should be added
What additional information should be included in the annotations of cell drawings?
The functions of organelles and cells should be included as part of the annotations in cell drawings.
