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B1 Cell Structure and Transport (Mricroscopes (Electron Mricroscope…
B1 Cell Structure and Transport
Mricroscopes
Light Microscopes
use a beam of light to form an image
can magnify up to x2000
but school microscopes only up to x400
objective lenses
x4, x10 and x40
magnification
eyepiece lens
x10
limited magnification
can view live speciments
relatively cheap
can be used anywhere
resolving power of 200nm
limited resolution
Electron Mricroscope
use a beam of electrons to form an image
magnify to to x2,000,000
greater magnification and resolution
cannot view living objects
can view subcellular structures
very expensive
cannot be used anywhere
very large
need to be kept in special conditions
i.e. temperature, pressure and humidity controlled rooms
Transmission Electron Mricroscope
gives 2D images
higher magnification and resolution
resolving power of 0.2nm
Scanning Electron Mricroscope
gives 3D images
lower magnification and resolution
resolving power of 10nm
Total magnification
=
Eyepiece lens magnification
x
Objective lens magnification
units
1mm = 1000μm
1μm = 1000nm
Magnification
=
Image size
÷
Real object size
Resolution
is the ability to distinguish two separate dots close together
resolving power
is a measure of resolution
affects how much detail it shows
Required Pratctical
place prepared slide onto
stage
and use
clips
to hold in place
select lowest power objective lens (x4)
turn the
coarse focussing dial
to move the objective lens down so that it almost touches microscope slide *view from the side
turn the
coarse focussing dial
, increasing the distance between objective lens and slide until the cells come into
focus *
view from eyepiece
turn the fine focusing dial to bring the cells to a clear focus
repeat using a higher power objective lens
draw a labelled diagram of the cells
in plant cells you should see the cell wall, cytoplasm and nucleus, sometimes vacuole and chloroplasts
in animal cells, we can see the nucleus, cytoplasm and cell membrane, sometimes mitochondria
include a
magnification scale
on your drawing
place a clear plastic ruler over stage and measure
diameter of field of view
in mm
show this on our drawing using a
scale bar
also write the magnification
Animal Cells
10μm to 30μm in size
Subcellular Structures
Nucleus
diameter 10μm
controls cell activities
surrounded by nuclear membrane
contains genetic material
carry instructions for building new cells
in genes on chromosomes
Cytoplasm
liquid gel which suspends the organelles
where most chemical reactions take place
Cell Membrane
controls the movement of substances in and out of the cell
glucose and mineral ions into cell
urea and hormones out of cell
Mitrochondria
very small
diameter 0.2-0.7μm
length 1-2μm
where aerobic respiration takes place
releases energy
Ribosomes
where protein synthesis takes place
makes proteins needed in the cell
Specialisation
cells
differentiate
to form different specialised cells
animal cells differentiate at an early stage in development
they get different subcellular structures
to carry out particular functions
specialised cells many work individually or as part of a tissue, organ or whole organism
Nerve Cells
carry electrical impulses around the body
Long Axon
carries the electrical impulse from one place to another
Myelin Sheath
insulates the axon to speed up transmissions
Synapses (nerve endings)
produce transmitter chemicals
pass impulses to other cells
lots of Mitochondria
transfers energy needed to produce transmitter chemicals
Lots of Dendrites
increase the SA
nerve cells can connect easily
Muscle Cells
contract and relax
Striated
(striped) muscle cells form muscle tissue that allow body movement
Special Protein Fibres
shorten to contract
they slide over eachother
Many Mitochondria
provide energy for muscle contraction
Stores Glycogen
a form of glucose
can be broken down and used in respiration
Smooth
muscle cells form the tissue in the gut which moves food along
work together to form muscle tissue
Sperm Cells
fertilises an ovum
Long Tail
whips side to side
movement through water or the female reproductive system
Middle Section
full of Mitochondria
provide energy for tail movement
Acrosome
stores digestive enzymes to break down outer layer of the egg
Large Nucleus
carries the genetic information from the male parent
contains only half the genetic information of a normal adult cell
Streamlined
for easier movement
Plant Cells
10μm to 100μm in size
larger than animal cells
regular shape
Subcellular Structures
plants also contain all the structures in an animal cell
Cell Wall
made from
cellulose
strengthens the cell
Chloroplasts
contain green
chlorophyll
absorbs light
sites of photosynthesis
makes food
root hair cells do not have chloroplasts
underground
do not photosynthesise
length 3-5μm
Permanent Vacuole
contains
cell sap
keeps cells rigid to give it shape
Algae are simple aquatic organisms with similar features to plant cells
classified as a
protist
eukaryotes
not a plant
contains chloroplasts to photosynthesise
contains a cellulose cell wall
contain all animal cell structures too
Speicalisation
many plant cells can differentiate throughout life
Root Hair Cells
Root Hair
increases the SA of the root
absorb water and mineral ions efficiently
found near tips of roots
close to the xylem tissue
Large Permanent Vacuole
speeds up movement of water by osmosis
Many Mitochondria
transfers energy needed for active transport of mineral ions
No Chloroplasts
underground so do not photosynthesise
Photosynthetic Cells
makes food for plant by photosynthesis
Chlorplasts
contain chlorophyll to trap light
Continuos Layers in leaves and outer stem
absorb as much light as possible
Large Permanent Vacuole
keeps cell rigid by osmosis
supports the stem
keeps leaves spread out to capture more light
Xylem Cells
makes up the Xylem transport tissue in the plant stem
carries water and mineral ions from
roots to shoots
supports the plant
Lignin
cells are alive when first formed
lignin (a chemical) builds up in spirals in the cell walls
the cell
dies
and the end wall between cells break down
forms long hollow tubes so water and mineral ions can move up through
no internal cell structure for easier flow
lignin
spirals
make the tubes very strong (thick walls)
withstands water pressure
supports plant stem
Phloem Cells
makes up the Phloem transport tissue
carries dissolved sugars
up and down
the plant
Phloem Vessel Cells
Sieve Plates
cell walls between phloem cells break down
allows food to move through the tube
Lose Internal Structure
no nucleus and limited cytoplasm
allows free and easy movement
Companion Cells
keeps the phloem vessel cells alive
phloem cells have little mitochondria
Mitochondria
provides energy to phloem cell to move foods up and down
Eukaryotic and Prokaryotic cells
Eukaryotic Cells
animals, plants, fungi and protists are eukaryotes
contain their genetic material enclosed in a nucleus
nucleus contains chromosomes made of DNA
contain a cell membrane and cytoplasm
Prokaryotic Cells
bacteria are prokaryotes
single-celled organisms
length 0.2-2μm
Subcellular Structures
*only some have these
Slime Capsule
protective layer
Flagellum (Flagella)
long protein strands
for movement
not all bacteria are harmful
but some cause disease
others decompose food
genetic material is not enclosed in a nucleus
contains a single loop of DNA
may also contain plasmids
small rings of DNA
code for special features i.e. antibiotic resistance
much smaller than eukaryotes
1-2 orders of magnitude smaller
only seen using a powerful microscope
bacterial colonies can be seen when bacteria multiplies
contains a cell membrane and cytoplasm
contains a (bacterial) cell wall
cell wall is not made of cellulose
different to plant cell walls
Orders of Magnitude
make approximate comparisons
shown using powers of 10
every order of magnitude is 10x larger than the previous
100 = 10² = two orders of magnitude
1000 = 10³ = three order of magnitude
10 = one order of magnitude
divide the larger no. by smaller no.
if <10 then = same order of magnitude
roughly to nearest power of 10
work out how many orders of magnitude difference
Diffusion
diffusion is the spreading out of particles of any substance, in solution or gas
net (overall) movement
down
a concentration gradient
concentration gradient
is the difference in concentration between two areas
from an area of high concentration to an area of low concentration
net movement
=
particles moving in
-
particles moving out
takes place because of random movement of particles
a passive process - no energy required
Rate of Diffusion
Concentration Gradient
the larger the difference in concentration, the
steeper
the concentration gradient so the faster the rate of diffusion
Temperature
the higher the temperature, the
faster
the particles move so the faster the diffusion rate
Surface Area
the larger the SA of the membrane, the
more substance
moves in a given time so the faster the rate of diffusion
In Living Organisms
Oxygen
gas exchange in the lungs to bloodstream
from bloodstream into body cells for respiration
Carbon Dioxide
gas exchange from bloodstream to lungs
from body cells to bloodstream
to photosynthesising plant cells
Glucose
from bloodstream into body cells for respiration
from gut (small intestine) to bloodstream
Urea
from liver to blood plasma
excreted by kidneys
Osmosis
osmosis is the diffusion of water
across a partially permeable membrane
partially permeable membranes
only let some types of particles through
from a dilute to a concentrated solution
concentrated
solution has a lower water concentration
down
a concentration gradient
dilute
solution has a high concentration of water
passive process - no energy needed
Solution Concentrations
Isotonic
two solutions have the same concentration
Hypertonic
the solution that is more concentrated
more solute and less water
Hypotonic
the solution that is more dilute
more water and less solute
Osmosis in Animals
cytoplasm contains a fairly
concentrated
solution of salts and sugars
inside a partially permeable cell membrane
Restoring Balance
if water lost in chemical reactions, cytoplasm becomes concentrated
surrounding fluid is
hypotonic
to cell and water moves into cell
if water made in chemical reaction, cytoplasm becomes dilute
surrounding fluid is
hypertonic
and water moves out of cell
if solution is
isotonic
to cell
there is no net movement of water in or out so cell is normal
Damages
cell surrounded by much more hypotonic solution
cell
swells
and may
burst
too much water moves into cell
cell surrounded by much more hypertonic solution
too much water moves out of cell
cell
shrivels
and
shrinks
Examples
water absorption in the large intestine into the bloodstream
reabsorption of water in the kidneys into the blood
Osmosis in Plants
osmosis is important to maintain
Turgor Pressure
in plant cells
water enters cell
vacuole swells
cytoplasm pressed against cell wall
cell wall prevents cell bursting
cells become rigid and turgid (normal)
leaves and stem are firm and rigid
surrounding fluid of cell must always be
hypotonic
to cytoplasm
Damages
cell surrounded by isotonic/ hypertonic solution
cells become
flaccid
(soft)
loses water
no turgor pressure
plant wilts
cell surrounded by much more hypertonic solution
more water loss
cell become
plasmolysed
vacuole and cytoplasm shrink
cell membrane pulls away from cell wall
cells die quickly
Required Practical
peel the potatoes then using a
cork borer
to make three potato cylinders with the same diameter
use a
scalpel
to trim cylinders to same length (3cm)
measure length and mass of potato cylinders using
ruler
and
mass balance
add 10cm³ of different concentrations of salt/sugar solutions to the 3 test tubes (0.5 molar, 0.25 molar and distilled water)
place a potato cylinder into each test tube and leave overnight to allow osmosis to take place
remove potato cylinders and
gently
roll on paper towel to remove any surface moisture
measure the length and the mass of the three cylinders agian
calculate the
percentage change
in length and mass of each potato
% change
=
(change in value
÷
original value)
x
100
plot a graph of concentration against % change in mass/length
where straight line crosses x-axis (0 % change) is the approximate concentration inside the cell
Examples
osmosis allows guard cells to open and close
water in soil diffuses by osmosis into root hair cells
water movement from cell to cell in plant
Active Transport
moves substances from an area of low concentration to an area of high concentration
against
a concentration gradient
across a
partially permeable membrane
requires
energy
from respiration
cells that carry out active transport have many mitochondria
transport proteins
in the cell membrane attaches to a useful molecule outside the cell
transport protein rotates using energy and releases molecule inside cell
transport protein rotates back to position using energy
In Living Organisms
Mineral Ions
found in very dilute solutions in soil
root hair cells absorb mineral ions from soil into plant
Glucose
absorbed from small intestine and kidney tubules into bloodstream
to get as much possible out of gut
initially absorbed using diffusion
Cystic Fibrosis
people have thick, sticky mucus
the active transport system of their mucus-producing cells do not work
Exchanging Materials
Surface Area : Volume ratio
as organisms increase in size, their SA:V ratio decreases
Small Single-Celled Organisms
relatively large SA:V ratio
simple diffusion
diffusion distances are short
all necessary exchange of materials happen through their surface
Large, Complex Organisms
many cells are not in contact with the environment
gases and food molecules can't reach every cell by simple diffusion
metabolic waste cannot be removes fast enough to avoid cell poisoning
Special
Exchange Surfaces
Large Surface Area
for exchange to take place
Thin Membrane
short
diffusion path
Efficient Blood Supply
maintains a
steep
concentration gradient
in animals
Ventilated
in gas exchange surfaces in animals
maintains a
steep
concentration gradient
air moving in and out
Adaptations
Alveoli (in lungs)
ventilated as air moves in and out
large SA
rich blood supply
gas exchange between air and blood
Villi (in small intestine)
large SA
short diffusion path
rich blood supply
absorbing soluble food molecules
Gills (in fish)
operculum (a flap) ventilates gills with flow of water
thin filaments
rich blood supply
gas exchange between water and blood
Leaves (in plants)
flat and thin for large SA
internal air spaces
maintain steep concentration gradient
stomata
gases move in and out
gas and solute exchange
Roots (in plants)
long and thin to increase SA
absorbing water and mineral ions from soil
root hair cells increase SA
