OCR AS Biology : Unit 1 (F212) : Cells, exchange and transport.

Cells B1 Workbook

Measuring Cells

There 3 types of microscope used to study cells: light microscope, transmission electron microscope (TEM) and Scanning electron microscope (SEM).

Modern light microscopes can achieve an effective magnification of up to 1500x and have a maximum resolving power of 200nm. Electron microscopes can achieve magnifications of up to 500000x and resolutions of 1nm.

The power of a microscope depends both on its magnification and resolution.

The higher the resolution of a microscope the greater the detail you can see.

Units of measurement

1) Complete the diagram below to show: names of the units of measurement, unit symbols, mathematical operations for converting between units.

2) Complete the table below to show the corresponding value nanometres, micrometres and millimetres for the measurements given in each row. The first row has been completed for you. Ensure that your answers use the correct unit symbols.

nanometremicrometremillimetre metre

50.0050.0000055 X 10-9

1

1

1

3

7

0.5

2.4 x 10-9

3) When studying cells structure using a microscope the smallest unit of measurement commonly used to describe findings is the nanometre. Explain why.

Magnification and Resolution

1) Define the following terms:

Magnification:

Resolution:

2) Visible light has a wavelength of 400-700 nm. Calculate the best resolution achievable with a light microscope? Show your working out:

3) If the electron gun produces an electron beam with 2 nm wavelength, what is the best resolution achievable?

Calculating total Magnification of a compound light microscope

Eyepiece MagnificationObjective MagnificationOverall Magnification

X10X4

X10X10

X10X40

X10X100

Calculating Cell Magnification from images

The diagram below shows the general structure of an animal cell as seen under an electron microscope. Label A H.

_________5m

1) Calculate the magnification factor of the diagram

2) Calculate the length of structure G

3) Calculate the diameter of the nucleolus (structure B)

4) Calculate the diameter of the nucleus

5) Calculate the diameter of the cell at its widest point

The diagram below shows the general structure of a plant cell when viewed under and electron microscope.

___________ 40m1) Calculate the magnification factor of the diagram

2) Calculate the thickness of the cellulose cell wall.

3) Calculate the length of the cell.

4) Calculate the length of structure C.

5) Calculate the length of the vacuole.Types of microscopeFeatureLight MicroscopeTransmission electron microscope (TEM)Scanning electron microscope (SEM)

Source of image

How is the beam focused

Maximum effectivemagnification

Maximum resolution

Can a live specimen be used?

Section or external view of the specimen

Cost

Can the image be viewed directly

Is staining of the specimen required?

1) Why is the maximum effective magnification of a light microscope said to be 1500x when it is possible to produce higher magnifications with improved lenses?

2) Use a named example to explain the need for staining when using a light microscope.

3) State a possible disadvantage of staining a specimen for observation when using a light microscope

4) State 2 advantages of using electron microscopes to study cells over a light microscope.

5) State 2 disadvantages of using electron microscopes to study cells.

6) Describe with reference to the role of staining how the transmission electron microscope differs from a scanning electron microscope?

7) Explain why a vacuum necessary in an electron microscope?

Which microscope?

1) State which type of microscope has been used to create the image below, give a reason for your answer.

2) The two images below of human chromosomes were produced using a light microscope and SEM. State which is which; give a reason for your answer.

3) The image below was produced by staining a section of gut epithelium. The image is not shown in false colour. Which type of microscope was used to produce the image? Explain your answer.

4) The three images below are of human cheek cells. One image has been produced using a light microscope, one using a SEM and one using a TEM. For each image identify the microscope used and justify your choice.

Cell structure

Key objectives: Which organelles may be present in a cell and why? How can we recognise organelles in micrographs / diagrams? What are the differences between prokaryotic and eukaryotic cells?

1) Name a type of human cell (not a sperm cell) that is able to move and explain why this is important to the cells function

2) Why might chloroplasts need to be moved around a plant cell

3) Many of the cells that line the human respiratory system are ciliated. Explain why

Which organelles may be present in a cell and what do they do?

Organelle Diagram StructureFunctionAnimal cell?Plant cell? Visible under a light microscope

Nucleus

NucleolusThe nucleus is the largest organelle (10-20m diameter)Roughly spherical.Surrounded by a double membrane called the nuclear envelopeThe nuclear envelope contains openings called nuclear pores.Outer membrane joins up to the endoplasmic reticulum The nucleoplasm contains chromatin (DNA + histones) which can be seen as dark blobs or fibre.)

Nucleolus is not surrounded by A membraneDense spherical structure inside the nucleusContains nearly all of a cells genetic material; instructions for making proteinsControls protein synthesis (makes mRNA)

Nucleolus makes RNA and Ribsosmes. These pass into the cytoplasm through the nuclear pores

Yes

Yes

Yes

Ribosome

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Golgi apparatus

Mitochondrion

(mitochondria)

Chloroplast

Lysosome

Centrioles

Plasma membrane

1) Describe three structures / organelles present in generalised plant cells but absent from animal cells. A) B) C)

2) Name the structures in the diagram below

3) Sperm cells contain large numbers of mitochondria. Explain why?

4) What evidence can be seen in the diagram that suggests that the cell is:

metabolically active and involved in secretion of enzymes [3]

involved in production or modification of lipids? [1]

The diagram is a line drawing of a cell as seen with an electron microscope. 20 mACDBEFGH

Complete the table by matching the label to the function and then naming the appropriate part. The first one has been completed for you.

Function of StructureLabelName of Part of the Cell

Controls the activity of the cell.ANucleus

Protein/polypeptides are made here.

Aerobic respiration takes place here.

Produces secretary vesicles.

Controls the entry of substances into the cell.

Contains hydrolytic enzymes.

Makes lipids, including steroids.

By reference to the diagram: Is the cell that of an animal or a plant? Give a reason for your answer.

Identifying organelles from micrographs

1) Name the large round organelle in the micrograph below 2) Is it found in animal or plant cells3) Name the structures A,B and C

4) Name the large organelle shown in the micrograph below5) Is it found in animal or plant cells?6) Suggest what structure D could be

7) Name the organelle shown in the micrograph below8) State the role of the organelle

9) Name the structures visible in the transmission electron micrographs below

10) Name the structure shown in the micrograph below

11) Name the structure shown in the micrograph below

Test yourself on a full cell micrograph

Is this an animal or plant cell? Can you name the structures 1-4

Parts of the cell working together

Complete the paragraph below to describe how organelles in a cell work together to produce and secrete proteins such as hormones

The nucleus carries all the necessary instructions for the cell to function. The code for protein synthesis is carried in the ____________ which are made of ____________ or histones. The instructions are ____________ or copied into mRNA (messenger ribonucleic acid). The mRNA then leaves the nucleus via the _________________ and travels to the ______________ where the message is read and translated into protein. The newly manufactured proteins are transported to forming face of Golgi body/apparatus in transport __________. Within the Golgi apparatus the proteins are processed. Vesicles are budded off from the maturing face of Golgi and are transferred to the ___________________ for secretion. Glandular cells (e.g. pancreas) contain large amounts of __________________ (this is encrusted with ribosomes and is where protein synthesis takes place) and Golgi body. These cells also contain many mitochondria since protein synthesis requires a lot of __________.

(ii) State the function of structures B. [1]

(iii) Describe the role of structure C in secretion. [3]

Prokaryotes and Eukaryotes

1) The diagram below shows Staphylococcus, which is a prokaryotic cell. Label parts A to D

2) The following table compares some features of a prokaryotic and eukaryotic animal cell. Complete the table by using present, absent or a short descriptive phrase. The first has been completed for you.

Cellular FeatureProkaryotic CellEukaryotic Animal Cell

Cell wallPresentAbsent

Cell surface membrane

Nucleus

Membrane bound organelles

DNA

Plasmids in the cytoplasm

1) Fill in the gaps

It was once common practice to classify all living organisms as either animals or plants. With improved knowledge of living things it has become apparent that there are ______ fundamentally different types of cell. The most obvious difference between the two types is that one possesses a nucleus and the other does not.

The cells of animals, ___________ and fungi contain many organelles some of which are bound by a membrane. These are referred to as ______________ cells. The cells of bacteria are very different, they lack membrane bound organelles such as a _____________. This type of cell is referred to as a _______________ cell (meaning before nucleus). Prokaryotic cells are about 1000 to 10000 times smaller than eukaryotic cells and are much simpler in structure. Biologists believe eukaryotes evolved from ________________.

2) Eukaryotic cells contain membrane bound organelles, give 5 examples:

3) Prokaryotic cells have one membrane, where is it?

4) Use table 1 to compare plant (eukaryote), animal (eukaryote) and prokaryotic cells. For each cell type indicate whether the feature is present or absent using a tick or cross.

FeaturePlant cellsAnimal cellsProkaryote cells

Chloroplasts

Large permanent vacuole

Cellulose cell wall

Peptidoglycan (murein) cell wall

Linear chromosome

Circular chromosome

Plasmids

Endoplastic Reticulum

Golgi body

DNA free in the cytoplasm

ATP is produced in the mitochondria

ATP is produced at infolded regions of the cell membrane called mesosomes

Undulipodia contain 9 + 2 circular arrangement of microtubules

Flagella made form spiral protein called Flagellin

Ribosomes

Cell membrane

5) Give 2 ways in which prokaryotes are useful to humans

6) Mitochondria and chloroplasts contain small loops of DNA similar to the plasmids found in prokaryotic cells. These organelles also contain ribosomes that are the same size as prokaryotic ribosomes. Can you suggest an explanation for these features?

7) Give one way in which a eukaryotic plant cell is similar to a prokaryote.

8) Give two ways in which a eukaryotic plant cell is different from a prokaryote.

9) Label the highlighted features on the diagram of the bacterium E.coli shown in the diagram below.

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