cell biology-part 1

What are eukaryotic cells?

Cells with genetic material (DNA) enclosed in a nucleus

● Plant and animal cells

What are prokaryotic cells?

Cells with genetic material (DNA) not enclosed in a nucleus

● Bacterial cells

● Much smaller in comparison

Describe the genetic material in a prokaryotic cells

A single loop of DNA

● May also have small rings of DNA called plasmids

What is an order of magnitude?

A power to the base 10 used to quantify and compare size

● 10 (10

1

) times bigger = 1 order of magnitude bigger, 100 times (10

2

) bigger = 2 order of magnitudes bigger

Describe the function of sub-cellular structures in animal and plant cells

1. Cell membrane Controls movement of substances in and out of cell

2. Cytoplasm Gel-like substance where chemical reactions take place

3. Nucleus Contains genetic material (DNA) → controls activities of cell

4. Mitochondria Site of aerobic respiration → releases energy from glucose

5. Ribosomes Site of protein synthesis

Describe the function of additional sub-cellular structures in plant cells

6. Cell wall Made of cellulose → strengthens cell (algal cells have one too)

7. Chloroplasts Contain chlorophyll → to absorb light for photosynthesis to make glucose

8. Permanent vacuole Filled with cell sap → help keep cell turgid / support plant

How could you estimate the relative size or area of sub-cellular structures?

Find a shape that resembles it → apply the rules normally used to calculate the size / area of that shape

Required practical activity 1

Use a light microscope to observe, draw and label a selection of plant and animal cells.

A magnification scale must be included.

Describe how to prepare a microscope slide

1 ● Plant eg. onion cells: peel off thin layer of tissue

using forceps, place a water drop on slide

● Animal eg. cheek cells: swab inside cheek with a

cotton bud, smear onto centre of slide

2 Add a drop of stain with a pipette

3 Lower coverslip at an angle without trapping air bubbles

Describe how to use a microscope to view cells

1 Clip slide onto stage and turn on light

2 Select lowest power objective lens (usually x 4)

3 a. Use coarse focusing dial to move stage close to lens

b. Turn coarse focusing dial to move stage away from

lens until image comes into focus

4 Adjust fine focusing dial to get clear image

5 Swap to higher power objective lens, then refocus

How is the total magnification of a microscope calculated?

How can the sizes of cells be estimated using a microscope?

What are the rules of scientific drawing?

Magnification of eyepiece lens x magnification of objective lens eg. 10 x 4 = x 40

1. Measure diameter of field of view (by using microscope to observe a transparent ruler)

2. Divide this by number of cells that span field of view

No sketching or shading - only use clear,

continuous lines (with a sharp pencil)

✓ Include a magnification scale (eg. x 400)

✓ Label important features eg. nucleus

Describe 3 examples of specialised cells in animals

Sperm cell -Fertilise an egg

● Long tail / flagellum → allows sperm to swim / move towards egg

● Many mitochondria → ↑ rate of respiration to release energy for swimming

Nerve cell-Carry electrical impulses

● Long → carry electrical impulses / signals over long distances

● Many branches → connect to many other cells forming a network

● Insulation → speeds up transmission of impulses

Muscle cell

Contract

● Many mitochondria → ↑ rate of respiration to release energy for contraction

Describe 3 examples of specialised cells in plants

Root hair cell

Absorb water & mineral ions from soil

● Long projection → ↑ surface area for absorption of water by osmosis

● Many mitochondria → ↑ rate of respiration to release energy for active

transport of mineral ions

Xylem cell

Transport water & mineral ions from roots to leaves

● Lignin in cell wall → strength to withstand pressure of water moving

● Hollow tubes / no cytoplasm → water / mineral ions move easily

● End walls between cells broken down → cells form a long tube so water /

mineral ions can flow easily

Phloem cell

Transport dissolved sugars up & down plant

● No nucleus → maximise space for movement of dissolved sugars

● Pores in end walls → dissolved sugars can move from cell to cell

What happens as a cell differentiates?

It acquires different sub-cellular structures

● To enable it to carry out a certain function

● So it has become a specialised cell

When do animal cells differentiate?

When do plant cells differentiate?

Most types differentiate at an early stage (embryo development)

● In mature animals, cell division is mainly restricted to repair and replacement (eg. new blood / skin cells)

Many types retain the ability to differentiate throughout life.

Why is cell differentiation important?

As an organism develops, cells differentiate to form different types of cells

● Specialised cells make different parts of the body / tissues / organs

What is the difference between magnification and resolution?

Magnification = number of times bigger image is compared to real object

● Resolution = shortest distance between 2 points that can be seen as separate points (level of detail)

What is the difference between light and

electron microscopes?

Light microscope:

Image formed using light

Electron microscope:

● Magnification higher

● Resolving power (resolution) higher

○ So can study cells in much finer detail / see more sub-cellular structures eg. ribosomes

List the steps in calculations involving magnification, real size & image size

1 Note formula / rearrange if necessary (I = AM)

2 Convert units if necessary - image and actual size

must be in same unit

3 Calculate answer and check units required or if

standard form is required

What are chromosomes?

How are chromosomes arranged in the nucleus of a body cell?

Tightly coiled strands of DNA molecules

● Found in nucleus of a cell

● Carries a large number of genes

(section of DNA that codes for a protein)

In pairs eg. humans - 23 pairs, 46 total

Why is cell division by mitosis important?

Parent cell divides to produce 2 genetically identical cells for...

○ Growth and development of multicellular organisms

○ Replacing (worn out or damaged) cells → repair damaged tissues

Give examples of contexts where mitosis is occurring

Regular replacement of skin cells, blood cells, cells lining digestive system

● Growth of embryos into foetuses and beyond

● Plant root / shoot tips

Describe the stages of the cell cycle, including mitosis

Stage 1

● DNA replicates to form 2 copies of each chromosome

● Cell growth - number of sub-cellular structures

increases such as ribosomes / mitochondria

Stage 2

(mitosis)

● One set of chromosomes is pulled to each end of cell

● Nucleus divides to form two nuclei

Stage 3

● Cytoplasm and cell membrane divide

● 2 genetically identical cells are formed

What is a stem cell?

An undifferentiated cell which can:

1. Give rise to many more cells of the same type

2. Differentiate into certain other cells

Describe the two types of animal stem cells

Embryonic stem cells

● Found in early embryos, can differentiate into any type of body cell

Adult stem cells

● Eg. found in bone marrow

● Can differentiate into many (not all)

types of cell, eg. blood cells

What are the potential uses of stem cells in medicine?

Embryonic stem cells

● Can be cloned and made to differentiate into most cell types

● Transplanted into patient to replace faulty / damaged cells

● Could treat (Type 1) diabetes (replace pancreas cells) and paralysis (replace nerve cells)

Adult stem cells

● Can only differentiate into some cell types

● So can treat a smaller variety of diseases eg. bone marrow transplant for blood cancer

What is therapeutic cloning?

What is the key advantage of therapeutic cloning?

Producing embryo with same genes as a patient (transfer patient cell nucleus to empty donor egg cell)

● Stem cells from embryo are stimulated to divide to form any cells the patient needs for medical treatment

Stem cells unlikely to be rejected by patient’s immune system

What are some issues associated with the use of stem cells in medicine?

Describe stem cells in plants

Transfer of viral infection

● Risk of rejection by immune system → have to take immunosuppressant drugs

● Ethical and religious objections eg. potential life destroyed / embryo cannot give consent

Found in meristem regions (growing regions) in roots and shoot tips

● Can differentiate into any type of plant cell, throughout a plant’s lifetime eg. xylem / phloem

How can stem cells from meristems in plants be used?

To produce clones of plants quickly and economically, for example:

● Rare species to protect from extinction

● Crop plants with special features eg. disease resistance → large numbers of identical plants for farmers