1.1 Cells

Light microscope

Light microscope

Equipment which uses visible light to detect and magnify small objects

Magnification

How much an image appears to have increased in size by

Magnification equation

Magnification = image size/actual size

Total magnification

The 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

lenses above the stage that can be manually adjusted for a higher magnification

Graticule

A scale with many divisions that is printed on to the eyepiece lens to measure an object's size

Focusing wheel

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

Microscope slide

thin piece of glass to hold specimens to be observed

Microscope stage

Where the microscope slide is placed with stage clips

Field of view

maximum area visible when looking through a microscope

Onion cells

An easily obtainable source of plant cells

Cheek cells

An easily obtainable source of animal cells

Iodine solution

An orange-brown dye that can be used to stain onion cells to make them easily observable

Methylene blue

blue dye to stain cheek cells to make them easily observable

Light microscope

Equipment which uses visible light to detect and magnify small objects

Electron microscope

forms an image by focusing beams of electrons, has a higher resolution and magnification than light microscopes

Importance of electron microscopes

increased understanding of sub-cellular structures such as ribosomes

Resolution

The degree of detail visible in an image

Magnification equation

Magnification = size of image/size of real object

Standard form

numbers are expressed as decimals between 1 and 10 and multiplied by a power of 10

Micro

10^-6

Nano

10^-9

Image size

The size of an object on an image after magnification

Actual size

The actual or real size of an object before magnification

Sub-cellular structures

Structures or organelles that are found in the cell

Staining techniques

use of dyes to better see cells under a light microscope

Micrometre

There are 1 000 micrometres in a millimetre and 1 000 000 micrometres in a metre

Scale bar

A means of visually indicating the magnification of an image

Animal cell

cell with a nucleus, nuclear membrane, cell membrane and mitochondria

Plant cell

cell with a nucleus, nuclear membrane, vacuole, cell membrane, mitochondria, chloroplasts and a cell wall

Bacterial cell

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

Cell membrane

Controls the entry of substances into and outside of the cell

animal, plant and bacterial cells

How is the cell membrane adapted?

It is selectively permeable, only allowing some substances in and out

Nucleus

Contains the genetic material

animal and plant cells

Ribosomes

Where protein synthesis takes place

Cytoplasm

contains organelles and is where chemical reactions take place

bacteria, plants and animals

Mitochondria

Where cellular respiration takes place

Permanent vacuole

space in cytoplasm filled with cell sap

plant cells

Plant cell wall

outside layer of cellulose which strengthens and supports

Bacterial cell wall

outer layer not made of cellulose

Plasmids

Small rings of extra DNA

bacterial cells

Chloroplasts

Contains chlorophyll and is where photosynthesis takes place

plant cells

Why are there no chloroplasts visible in this photograph

It is a root cell, which contains no chloroplasts

Chlorophyll

green pigment in the chloroplast to absorbs light energy

What is magnesium ions used for?

to make chlorophyll

DNA loop

single molecule of DNA that is found free in the cytoplasm

bacterial cells

Flagella

long whip-like filament to aid movement

bacterial cells

Stem cell

An undifferentiated cell which can become any type of cell

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

Undifferentiated

A cell which is not yet specialised

Differentiated

has changed to specialise a specific function

Human embryo

source of stem cells which can become any type of cell

Umbilical cord

potential source of embryonic stem cells

Bone marrow

source of stem cells which can become most types of cell

Meristem

where mitosis occurs and source of stem cells in apices, used in cloning techniques

Apices

A term used to describe the tips of shoots or roots

Diabetes

disease of the pancreas which may be treated with stem cells

Spinal cord injury

cause of paralysis which may be treated with stem cells

Therapeutic cloning

embryo is produced with the same genes as the patient

Cloning rare plant species

A way of protecting from extinction using meristems

Cloning disease resistant crops

A way of providing food security, using meristem tissue

Zygote

fertilised egg cell which divides to form an embryo

Ethical or religious objections

Moral or religious reasons people may be against stem cell treatments

General issues of stem cells

1. Stem cells can lead to cancer or tumour formation

2. pre-treatment of stem cells involves risky procedures

3. possible transfer of spreadable diseases

4. anti-rejection drugs must be taken

5. left vulnerable to other illnesses

Advantages of bone marrow stem cells

1. treat leukaemia

2. less ethical concerns than embryonic

3. easier to obtain

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 bone marrow stem cells

1. voluntary donors,

2. extraction can cause pain and requires consent

3. may have a risk of infection,

4. can only form cells such as blood cells

5. risk of rejection

Disadvantages of embryonic stem cells

1. potential loss of life or harm to embryo

2. less easily obtained

3. risk of rejection

Sperm cell

animal cell with a head containing genetic material for fertilisation and a tail for swimming to the egg cell

Nerve cell

An extended animal cell with many branches that sends electrical messages around the body

Muscle cell

An animal cell that contains sliding protein fibres to contract and allow movement

Red blood cell

An animal cell that has lost its nucleus to make remove for haemoglobin, a protein that binds to oxygen

Intestinal epithelial cell

An animal cell that is responsible for molecule absorption in the intestines, these cells have many tiny folds called microvilli that increase the surface area for absorption

Root hair cell

large surface area and thin walls to absorb water and minerals

Cell differentiation

cells change shape and structure to produce different functions

Cell

basic building block of all living organisms

Tissue

A group of cells with a similar structure and function, such as muscular tissue or skeletal tissue

Organ

Collections of tissues performing specific functions, such as the brain or heart

Organ system

A system of organs which work together to form organisms, such as the circulatory system or digestive system

Organism

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

Multicellular

Organisms that are made of multiple cells

Need for transport systems

larger cells are unable to directly obtain substances

Transport system

used for transporting substances around multicellular living organism

Surface area

The total area of the surface of an object

Surface area to volume ratio

The amount of surface area in relation to how large something is

Large surface area to volume ratio

faster diffusion rates, as more room to diffuse through membrane

Diffusion

movement of substances from a higher concentration to a low

Gas exchange

When oxygen and carbon dioxide move in and out of cells by diffusion

Purpose of gas exchange

supply oxygen for aerobic respiration, remove carbon dioxide (waste product)

Sites of gas exchange

The alveoli and respiring cells

An effective exchange surface

• Has a large surface area

• a good blood supply

• well ventilated for gas exchange

• has a thin membrane for diffusion

Structures adapted for exchanging materials

Small intestine, kidneys, lungs, gills in fish, roots and leaves in plants

Specific cells, tissue and sacs adapted for exchange

Alveoli, ciliated epithelial cells, root hair cells

Dissolved food molecules

essential for cell functions and need to be transported by the blood

Gas exchange in plants

regulated by guard cells that open/ close stomata

Lungs

Are specialised in gas exchange due to the presence of many tiny sacs called alveoli that are adapted for diffusion due to being moist, one cell thick and surrounded by capillaries

Diffusion

The movement of substances such as gas particles or substances in solution, from a higher concentration to a lower concentration