1.1 Cells and Magnification

Light microscope

uses light to detect and magnify small objects

Using a light microscope

• start with low power objective lens as field of view is wider, allowing you to see and locate more cells

• once centred, switch to higher power lens for detailed viewing

Magnification

How much an image appears to have increased in size by

Total magnification

overall magnification of the eyepiece and the objective lenses

Total magnification equation

Total magnification = eyepiece magnification x objective lens magnification

Eyepiece lens

closest to the eye when viewing

Objective lenses

above stage that can be manually adjusted for higher magnification

Graticule

scale with many divisions on eyepiece lens to measure object's size

Focusing wheel

twistable wheel to adjust focus of object by changing height of stage

Microscope slide

thin piece of glass to hold specimens when observed

Microscope stage

Where slide is placed with stage clips

Field of view

maximum area visible when looking through a microscope

Drawing cell structures

• Drawn in pencil with firm, continuous lines (no sketching)

• Large and proportionate to observed cell

• Clearly labelled

• Given title with magnification or size

Electron microscope

focuses beams of electrons for a higher resolution and magnification than light microscopes

Importance of electron microscopes

• clearer and more detailed view of cells (ribosomes)

• revealing structures of smaller organelles (mitochondria/ chloroplast)

Resolution

degree of detail visible in an image

Magnification equation

Magnification = Image size/ Actual size

Micrometre (μm)

10^-6

Micrometres to millimetres

1000μm = 1mm

Image size

size of object after magnification

Actual size

real size of object before magnification

Sub-cellular structures

Structures or organelles that are found in the cell

Staining techniques

using dyes to better see cells by making parts more obvious e.g iodine/ methylene blue

Scale bar

• Measure length of scale bar using ruler

• Convert to micrometres

• Calculate magnification (measured length/ given length)

Animal cell

has a nucleus, nuclear membrane, cell membrane, mitochondria and cytoplasm

Plant cell

has a nucleus, nuclear membrane, vacuole, cell membrane, mitochondria, chloroplasts, cell wall and cytoplasm

Bacterial cell

has a cell wall, no nucleus as genetic material is free within cytoplasm/ plasmids, flagella (tail)

Cell membrane

Controls the entry of substances into and outside of the cell

How is the cell membrane adapted?

selectively permeable, only allowing some substances in and out

Nucleus

Control centre of cell which contains genetic information in the form of chromosomes

Cytoplasm

contains organelles and is where chemical reactions take place

Ribsomes

responsible for synthesising proteins

Mitochondria

Where cellular respiration takes place, abundant in cells requiring energy

Permanent vacuole

filled with cell sap and pushes cell membrane to provide support

Cell wall

rigid outside structure which strengthens and supports cell

Material of cell wall

plant cells are cellulose while bacterial are non-cellulose

Plasmids

Small circular rings of DNA in cytoplasm

Chloroplasts

Contains chlorophyll and is where photosynthesis takes place

Why are there no chloroplasts visible in this photograph

It is a root cell, which contains no chloroplasts

Chlorophyll

green pigment in the chloroplast which absorbs light energy for photosynthesis

What is used to make chlorophyll for?

magnesium ions

DNA loop

single molecule of DNA free in cytoplasm

Flagella

long whip-like filament to aid movement

Stem cell

undifferentiated cell which can divide to form cells of the same type and differentiate

What happens to stem cells when the are transported into the body?

they divide and differentiate into new white blood cells

Pre-treatments of stem cells

1. chemotherapy

2. radiotherapy

3. kills cancer cells

4. also kills normal white blood cells and other healthy cells

5. reduces immunity making them more susceptible to infection

6. side effects- can divide to form tumours

Differentiated

change to specialise a specific function

Embryonic stem cells

can become any type of cell, found in umbilical cord

Bone marrow stem cells

can become a limited range of cells (blood cells)

Meristem

where mitosis occurs and source of stem cells in apices

Apices

A term used to describe the tips of shoots or roots

How are plant stem cells useful

adult plant stem cells retain ability to differentiate to any type of cell

• useful for cloning techniques, helping to protect rare species from extinction

• modified disease resistance crops

Uses of stem cells

• produce insulin cells for diabetes

• treat paralysis from spinal cord injuries

Therapeutic cloning

embryo is produced with the same genes as the patient

General issues of stem cells

1. Lead to formation of tumours or unwanted cell types

2. Pre-treatments (chemo/radiotherapy) involves risky procedures

3. possible transfer of spreadable viruses or diseases

4. anti-rejection drugs must be taken

5. left vulnerable to other illnesses

6. ethical or religious objections

Advantages of bone marrow stem cells

1. treat leukaemia

2. less ethical concerns than embryonic

3. easier to obtain

Disadvantages of bone marrow stem cells

1. requires voluntary donors

2. extraction can cause pain and requires consent

3. may have a risk of infection or rejection

4. can only form cells such as blood cells

Advantages of embryonic stem cells

1. No consent required

2. obtainable via discarded embryos in IVF

3. can be used to make any type of cell

4. less risk of rejection if using therapeutic cloning

Disadvantages of embryonic stem cells

1. potential loss of life or harm to embryo

2. less easily obtained

3. risk of rejection

4. moral or ethical objections

Cell

basic building block of all living organisms

Cells adapted to their function

• nerve cell- long fibre to carry signals across large distances

• sperm cell- tail to move them towards egg cell

• red blood cell- no nucleus to provide space for haemoglobin

• root hair cell- long thin extension to increase surface area for absorption

Tissue

group of cells with similar structure and function working together

Organ

Collections of tissues performing specific functions

Organ system

group of organs which work together to form organisms

Organism

living thing such as a plant, animal or single-celled life form

Single celled

all life process carried out by one cell

Multicellular

made of multiple cells that differentiate to perform specific functions

Need for transport systems

larger cells are unable to directly obtain substances

Transport system

used for transporting substances around multicellular living organism

Surface area

total area of the surface of an object

Surface area to volume ratio

amount of surface area in relation to how large and object is

Large surface area to volume ratio

faster diffusion rates, as more room to diffuse through membrane

Diffusion

random movement of substances from an area of high concentration to a low e.g gas exchange

Adapted for exchanging materials

Small intestine- ciliated epithelial cells

lungs- alveoli

plant roots/ leaves- root hair cells

Passive process

Substances cross membrane without energy input from the cell

Net movement

overall movement of particles in diffusion

Concentration gradient

difference in concentration of a substance, a steeper gradient has faster diffusion

effect of temperature on diffusion

provide the particles with more kinetic energy, causing them to move, speeding up diffusion