basic components of living systems Flashcards
1
Q
What 3 things does Cell Theory state?
A
• Both plant and animal tissue is composed of cells • Cells are the basic unit off all life • Cells only develop from existing cells
2
Q
Define ‘compound light microscope
A
A light microscope which uses two lenses to magnify an object; the objective lens, which is placed near to the specimen and an eyepiece lens, through which the specimen is viewed.
3
Q
A
4
Q
List the 4 ways of preparing a sample for examination by light microscopy
A
List the 4 ways of preparing a
sample for examination by light
microscopy
5
Q
Describe the dry mount sample preparation method
A
• Solid specimens are viewed whole or cut into very thin slices (sectioning) • Specimen placed in centre of slide and cover slip is placed over the sample • e.g. hair, pollen, dust, insect parts; muscle tissue or plants can be sectioned and viewed this way
6
Q
Describe the wet mount sample preparation method
A
• Specimen are suspended in liquid e.g. water or oil • Cover slip is placed on from an angle • E.g. aquatic samples and other living organisms
7
Q
Describe the squash slides sample preparation method
A
• Wet mount is prepared first • Lens tissue is used to gently press down cover slip • Squash sample between 2 microscope slides to avoid damage to coverslip • Good technique for soft samples • e.g. root tip squashes are used to look at cell division
8
Q
Describe the smear slides sample preparation method
A
Edge of slide is used to smear sample creating thin even coating on another slide • Cover slip then placed over sample • E.g. for sample of blood to view cells in the blood
9
Q
Give 3 reasons why stains are used in samples in light
microscopy
A
• Images tend to have low contrast as most cells don’t absorb lots of light • The cytosol (aqueous interior) of cells and other cell structures are often transparent • Stains increase contrast as different components in the cell take up stains to different degrees
10
Q
How do you prepare a sample for staining?
A
• Place the sample on a slide and allow it to air dry • Heat fix the sample by passing through a flame • The specimen will adhere to the microscope slide and will then take up stains
11
Q
List and describe 4 different types of stains
A
Crystal violet & Methylene blue are \+ve dyes attracted to and staining cell components • Nigrosin & Congo red are negatively charged dyes that are repelled by the -ve cytosol so stay outside cells
12
Q
Define differential staining
A
Using specific stains to distinguish
different types of cell
13
Q
Describe the gram stain technique
A
• Used to separate bacteria into gram-positive and gram-negative bacteria • Crystal violet is first applied to a bacterial specimen on a slide, then iodine which fixes the dye, then the slide is washed with alcohol
14
Q
What are the 2 types of bacteria in gram staining?
A
• Gram negative bacteria - Bacteria with cell walls that stain red with Gram stain • Gram positive bacteria - Bacteria with cell walls that stain purpleblue with Gram stain
15
Q
What is the acid-fast technique?
A
• Used to differentiate species of Mycobacterium • Lipid solvent is used to carry carbolfuchsin dye into the cells, which are then washed with dilute acid-alcohol solution • Mycobacterium are not affected by the acid-alcohol and retain the carbolfuchsin stain which is bright red
16
Q
Define magnification
A
The number of times larger an image
appears, compared with the size of
the object
17
Q
Define resolution
A
The clarity of an image; the high the
resolution, the clearer the image
18
Q
What is the formula for calculating magnification?
A
Magnification = size of image /
. actual size of object
19
Q
In a light microscope, what is resolution limited by?
A
The diffraction of light as it passes through samples (and lenses). • Diffraction is the tendency of light waves to spread as they pass close to physical structures • Light reflected from individual structures can overlap due to diffraction • Structures are no longer seen as separate entities and detail is lost • In optical microscopy, structure closer than 1/2 the wavelength of light can’t be seen separately
20
Q
Why does using electron beams instead of light produce a better resolution?
A
Beams of electrons have a wavelength thousands of times shorter than light, so they are still diffracted, but individual beams can be a lot closer before they overlap. Therefore objects that are smaller and closer together can be seen separately without diffraction blurring the image
21
Q
What is an eyepiece graticule?
A
A glass disc marked with a fine scale of 1 to 100. The scale has no units. The scale on the graticule at each magnification is calibrated using a stage micrometer
22
Q
What is a stage micrometer?
A
A microscope slide with an accurate scale in micrometers marked on it. The scales usually 100 divisions = 1mm, so 1 division = 10 micrometers
23
Q
What are the steps in using a graticule to calibrate a light microscope?
A
For each objective lens: 1. Put stage micrometer in place and the eyepiece graticule in the eyepiece 2. Get the scale on the micrometer slide in clear focus 3. Align the micrometer scale with the scale in the eyepiece. Take a reading from the 2 scales
24
Q
Give the equation that links measurement (micrometers), graticule divisions, and
magnification factor
A
Measurement (micrometers) =
Graticule divisions x magnification
factor
25
Define ‘electron microscopy’
```
Microscopy using a microscope that
uses a beam of electrons to
illuminate a specimen. As electrons
have a smaller wavelength than
light, they produce images with
higher resolutions.
```
26
Describe electron microscopes
```
• Use beam of fast-travelling
electrons with wavelength < 1nm
to illuminate the specimen
• Electrons fired from a cathode and
focused by magnets onto screen
or photographic plate
• Produce images with
magnification up to x500 000 and
still have clear resolution
• Show more detail of cell
ultrastructure because electrons
have shorter wavelengths
```
27
What are the 2 types of electron microscope? Describe
| both.
```
Transmission Electron Microscope
• Beam of electrons transmitted
through a specimen and focused
to produce an image
• Specimen must be chemically
fixed by being dehydrated and
stained then thinly sliced
• 2D grey scale image is produced
• Best resolving power (0.5nm)
• Can produce magnification up to 2
million times
Scanning Electron Microscope
• Beam of electrons sent across
surface of specimen; reflected
electrons focused onto a screen
• 3D grey scale image
• Resolving power (3-10nm)
• Magnification x15 to x200 000
```
28
Summarise light microscopes/microscopy
```
• Inexpensive to buy and operate
• Small and portable
• Simple sample preparation
• Sample preparation doesn’t
usually lead to distortion
• Vacuum is not required
• Natural colour of sample is seen
(or stains are used)
• Up to x2000 magnification
• Resolving power is 200nm
• Specimens can be living or dead
```
29
Summarise electron microscopes/ miscroscopy
```
• Expensive to buy and operate
• Large and needs to be installed
• Complex sample preparation
• Sample preparation often distorts
material
• Vacuum is required
• Black and white images produced
(but can be coloured digitally)
• Over x500 000 magnification
• Resolving power of TEM is 0.5nm
and of SEM is 3-10nm
• Specimens are dead
```
30
What are artefacts?
```
Objects or structures seen through a
microscope that have been created
during the processing of the
specimen e.g. air bubbles trapped
under coverslip in light microscopy
```
31
How is electron microscopy affected by artefacts?
```
When preparing specimen, changes
in the ultrastructure of cells are
inevitable in the processing that
sample must undergo.
e.g. loss of continuity in membranes,
distortion of organelles and empty
spaces in the cytoplasm of cells
```
32
Define a ‘laser scanning microscope’
A microscope that employs a laser
beam and a pin-hole aperture to
produce an image with a very high
resolution
33
Describe laser scanning microscopes
```
• Use laser light to scan an object
point by point and assemble (by
computer) the pixel information
into 1 image displayed on a
computer screen
• High resolution images that show
high contrast
• Have depth selectivity and can
focus on structures at different
depths within a specimen
```
34
Give 3 instances in which laser scanning confocal
| microscopes are used
```
• To clearly observe whole living
specimens as well as cells
• Used in many branches of
biological research
• Used in medical profession e.g. to
observe fungal filaments within
cornea of the eye of a patient with
a fungal cornea infection, so that
diagnosis is earlier and treatment
is more effective
```
35
What are eukaryotes?
Multicellular organisms like animals,
plants, fungi and single-celled
protoctista
36
What are eukaryotic cells?
Cells with a nucleus and other
| membrane-bound organelles
37
38
Describe the structure of the plasma membrane
```
• The membrane found on the
surface of animal cells and just
inside the cell walls of plant cells
and prokaryotic cells
• Mainly made of lipids and proteins
```
39
What is the function of the plasma membrane?
```
• Regulates the movement of
substances into and out of the cell
• Also has receptor molecules on it,
which allow it to respond to
chemicals like hormones
```
40
Describe the structure of the nucleus
```
• Large organelle surrounded by a
nuclear envelope (double
membrane), which contains many
nuclear pores
• Contains coded genetic
information in the form of DNA
molecules
• Contains chromatin (made from
DNA and proteins called histones)
• Often contains a nucleolus
```
41
What is the function of the nucleus?
```
• Controls the cell’s activities (by
controlling DNA transcription)
• DNA controls the metabolic
activities of the cell
• Provides the instructions for
protein synthesis
• The pores allow mRNA to leave
the nucleus and substances e.g.
steroid hormones to enter
• Chromatin coils and condenses to
form chromosomes which contain
the organism’s genes
```
42
Describe the structure of the nucleolus
• An area within the nucleus
• Does not have an membrane
around it
• Composed of proteins and RNA
43
What is the function of the nucleolus?
```
• RNA is used to produce ribosomal
RNA (rRNA) which is combined
with proteins to form the
ribosomes necessary for protein
synthesis
```
44
Describe the structure of the rough endoplasmic reticulum (RER)
```
• Network of membranes containing
fluid-filled cavities called cisternae
• Connected to the outer membrane
of the nucleus
• Coated with ribosomes
• Secretory cells have more RER
than cells that don’t release
proteins
```
45
What is the function of the rough endoplasmic reticulum?
```
Responsible for the synthesis and
transport of proteins
• Intracellular transport system:
cisternae form channel for
transporting substances within the
cell
• Large surface area for ribosomes
which assemble proteins than then
actively pass through the
membrane into the cisternae and
are taken to the Golgi apparatus
```
46
Describe the structure of the smooth endoplasmic reticulum
• Network of membranes containing
fluid-filled cavities called cisternae
• No ribosomes on its surface
47
What is the function of the smooth endoplasmic
| reticulum?
```
• Responsible for lipid and
carbohydrate synthesis, and
storage
• Contains enzymes that catalyse
reactions involved with lipid
metabolism
```
48
Describe the structure of the Golgi apparatus
Consists of a stack of fluid-filled,
membrane-bound flattened sacs
• Vesicles are often seen at the
edges of the sacs
49
What is the function of the Golgi apparatus?
• Processes and packages new
lipids and proteins
• Makes Lysosomes
50
Describe the structure of mitochondria
```
• Surrounded by two membranes
(double membrane) with a fluidfilled
space between them
• Inner membrane is highly folded
into cristae, and the fluid interior is
called the matrix
• Membrane forming the cristae
contains the enzymes used in
aerobic respiration
```
51
What is the function of mitochondria?
```
• The site of ATP production during
aerobic respiration
• Contain mitochondrial (mt) DNA
and so can produce their own
enzymes and reproduce
themselves
```
52
Describe the structure of chloroplasts
```
• Large organelles
• Found only in plant cells and in
some protoctists
• Surrounded by a double
membrane
• Internal network of membranes
which form flattened sacs called
thylakoids that contain chlorophyll
• Each pile of thylakoids is called a
grana (pl. granum)
• Fluid enclosed in the chloroplast is
called the stroma
• Contain loops of DNA and starch
grains
```
53
What is the function of chloroplasts?
```
• The site of photosynthesis
• Internal membranes give large
surface area needed for the
enzymes, proteins and pigment
molecules in photosynthesis
• Stage 1: Light energy is trapped
by chlorophyll and used to make
ATP. Water is split into hydrogen
ions. Happens in the grana
• Stage 2: Hydrogen reduces CO2
using energy from ATP, to make
carbohydrates. Happens in the
stroma
```
54
Describe the structure of vacuoles
```
• Membrane lined sacs in the
cytoplasm containing cell sap
• Only plant cells have a permanent
vacuole (some animal cells have
transient vacuoles)
• Membrane of a vacuole in a plant
cell is called the tonoplast
```
55
What is the function of vacuoles?
```
• Filled with water and solutes, and
maintains cell stability because
when full it pushes against cell
wall, making the cell turgid
• The membrane is selectively
permeable
• Turgid plant cells helps to support
the plant, esp in non-woody plants
```
56
Describe the structure of lysosomes
```
• Specialised forms of vesicles that
contain hydrolytic (digestive)
enzymes
• Each is surrounded by a single
membrane
```
57
What is the function of lysosomes?
```
• Keep the powerful hydrolytic
enzymes separate from the rest of
the cell
• Responsible for breaking down
waste material in cells e.g. old
organelles and foreign matter
• Digest waste material then return
digested components to the cell
for reuse
• Play an important role in apoptosis
(programmed cell death)
```
58
Describe the structure of cilia
```
Small hair-like structs that
protrude from some cell types
• Each cilium contains two central
microtubules surrounded by 9
pairs of microtubules arranged like
a wheel
• Pairs of parallel microtubules
slipover each other causing the
cilia to move in a beating motion
```
59
What is the function of cilia?
```
Stationary cilia have an important
function in sensory organs e.g. the
nose
• Mobile cilia beat in a rhythmic
manner, creating a current and
causing fluids or close objects to
move, e.g. in the trachea moving
mucus away from the lungs
```
60
Describe the structure of flagella
```
Whip-like extensions that protrude
from some cell types
• Stick out from the cell surface and
are surrounded by the plasma
membrane
• 2 microtubules in the centre and 9
pairs around the edge
```
61
What is the function of flagella?
```
• Microtubules contract to make the
flagellum move
• Used primarily to enable cells
motility, e.g. when a sperm swims
• In some cells they are used as a
sensory organelle detecting
chemical changes in the cell’s
environment
```
62
Describe the structure of the cytoskeleton
```
• Network of fibres
• 3 components:
• Microfilaments - contractile fibres
formed from the protein actin
• Microtubules - globular tubulin
proteins polymerise to form tubes
• Intermediate fibres
```
63
What is the function of the cytoskeleton?
```
• Network of fibres necessary for the
shape and stability of a cell
• Holds organelles in place, controls
cell movement, and the movement
of organelles within cells
• Microfilaments - Responsible for
cell movement and cell contraction
during cytokinesis
• Microtubules - Form a scaffold-like
structure that determines the
shape of the cell. Act as tracks for
the movement of organelles,
including vesicles around the cell.
Spindle fibres are made of
microtubules
• Intermediate fibres - Give
mechanical strength to cells ad
help maintain their integrity
```
64
Describe the structure of centrioles (*not in flowering
| plants and most fungi)
```
• 2 bundles of microtubules at right
angles to each other
• The microtubules are made of
tubulin protein subunits and are
arranged to form a cylinder
```
65
What is the function of centrioles?
```
• 2 associated centrioles form the
centrosome, which is involved in
the assembly and organisation of
spindle fibres during cell division
• In organisms with cilia and flagella,
centrioles play a role in the
positioning of these structures
```
66
Describe the structure of ribosomes (* mitochondria,
| chloroplasts and prokaryotic cells also contain ribosomes)
```
Can be free-floating in the
cytoplasm or attached to the ER,
forming RER
• Not surrounded by a membrane
constructed by of RNA molecules
made in the nucleolus
```
67
What is the function of ribosomes?
```
• Site of protein synthesis
• On the RER are mainly for
synthesising proteins that will be
exported outside the cell
• Free in the cytoplasm are mainly
for assembling proteins that will be
used inside the cell
```
68
Describe the structure of the cellulose cell wall (*fungi have cell walls that contain chitin not cellulose)
```
• On the outside of the plasma
membrane
• Made from bundles of cellulose
(complex carbohydrate) fibres
• Contain plasmodesmata
```
69
What is the function of cellulose cell walls?
```
• Permeable and allow solutions to
pass through
• Provide strength and support for
cell and plant + maintain the cell’s
shape
• Defence mechanism, protecting
the cell from pathogens
```
70
Describe the structure of vesicles
• Membranous sacs
• A single membrane with fluid
inside
71
What is the function of vesicles?
• Storage and transport roles
• Used to transport materials inside
the cell
72
List all of the components of a eukaryotic cell
* Cytosol
* Plasma membrane
* Nucleus
* Nucleolus
* Rough endoplasmic reticulum
* Smooth endoplasmic reticulum
* Golgi apparatus
* Mitochondria
* Chloroplasts (plants)
* Vacuoles (mostly plants)
* Lysosomes
* Flagella
* Cytoskeleton
* Centrioles
* Ribosomes
* Cell wall (cellulose and chitin )
* Vesicles
73
```
1. Proteins are synthesised on the
ribosomes bound to the ER
2. They then pass into the cisternae
and are packaged into transport
vesicles
3. vesicles containing newly
synthesised proteins move
towards the GA via the transport
function of the cytoskeleton
4. Vesicles fuse with cis face of GA
and the proteins enter
5. The proteins are structurally
modified before leaving GA in
vesicles from its trans face
6. Secretory vesicles carry proteins
tone taken out of the cell; the
vesicles move towards and fuse
with cell surface membrane
releasing their contents by
exocytosis
7. Some vesicles form lysosomes
that contains enzymes for use in
the cell
```
74
What are prokaryotes?
```
Single-celled prokaryotic organisms
from the kingdom Prokaryotae. They
first appeared 3.5 billion years ago
and can be classed into either
Archaea or Bacteria
```
75
What are prokaryotic cells?
Cells a relatively simple structure w
with no membrane-bound nucleus,
and few organelles which are also
not membrane-bound.
76
77
Describe DNA in prokaryotic cells
```
• The structure of DNA is
fundamentally the same as in
eukaryotic cells, but packed
differently
• Only 1 molecule of DNA,a
chromosome, which is supercoiled
to make it more compact
```
78
Describe ribosomes in prokaryotic cells
```
• Smaller than those in eukaryotic
cells (70S vs 80S)
• Both types of ribosome are
necessary for protein synthesis,
but 80S are involved in more
complex proteins
```
79
Describe the cell wall in prokaryotic cells
• Made from peptidoglycan (also
known as murein)
• Complex polymer formed from
amino acids and sugars
80
Describe flagella in prokaryotic cells
```
• Thinner than those in eukaryotes,,
and doesn’t have the 9+ 2
arrangement
• Energy to rotate the filament that
forms the flagellum comes from
chemiosmosis not ATP as in
eukaryotic cells
• A molecular motor causes the
flagellum to rotate giving it a whiplike
movement that propels the cell
```
81
```
Summarise the differences
between prokaryotic and
eukaryotic cells:
• Nucleus
• DNA
• DNA organisation
• Extra chromosomal DNA
• Organelles
• Cell wall
• Ribosomes
• Cytoskeleton
• Reproduction
• Cell type
• Cell-surface membrane
```
