Cell Structure Flashcards

All 49 cards in this deck

What is a eukaryotic cell?

A cell whose genetic material is enclosed in a nucleus, and which also has a cell membrane and cytoplasm.
e.g. all plant and animal cells

What structures does a prokaryotic (bacterial) cell have?

Cytoplasm and a cell membrane surrounded by a cell wall, plus ribosomes; its genetic material is not enclosed in a nucleus.

Give the similarities between a prokaryotic cell and a eukaryotic cell.

Both have cytoplasm, a cell membrane, ribosomes and DNA (genetic material).

Roughly how does the size of a bacterial cell compare with the size of a plant or animal cell?

Bacteria are much smaller: about $1\ \mu$m across, compared with about $10$–$100\ \mu$m, so 1–2 orders of magnitude smaller.

True or false? The cell wall of a bacterium is made of cellulose, just like a plant cell wall.

False. Only plant and algal cell walls are made of cellulose; a bacterial cell wall is made of different material.

What parts are found in most animal cells?

A nucleus, cytoplasm, a cell membrane, mitochondria and ribosomes.

What is the function of the nucleus?

It contains the genetic material (chromosomes/DNA), which controls the activities of the cell.

What is the function of mitochondria?

They are where aerobic respiration takes place, releasing energy for the cell.

What is the function of the cell membrane?

It controls the movement of substances into and out of the cell.

What is the function of ribosomes?

Protein synthesis — they are where proteins are made.

What structures do plant and algal cells have in addition to the parts found in animal cells?

Chloroplasts (photosynthesis), a permanent vacuole filled with cell sap, and a cell wall made of cellulose that strengthens the cell.

What is a specialised cell?

A cell whose structure and sub-cellular structures allow it to carry out one particular function.

How is a sperm cell specialised for its function?

It has a tail to swim to the egg, many mitochondria to release the energy for swimming, and enzymes in the head to digest the egg's membrane.

How is a nerve cell specialised for its function?

It is very long, so impulses are carried over long distances, and has branched endings to connect to other cells.

How is a muscle cell specialised for its function?

It contains long protein fibres that can contract (shorten) and many mitochondria to release the energy needed.

What does it suggest about a cell if it contains a large number of mitochondria?

The cell is very active and needs a lot of energy released by aerobic respiration.

True or false? Every cell in a multicellular organism contains exactly the same sub-cellular structures.

False. Specialised cells have different sub-cellular structures suited to their particular function.

What is cell differentiation?

The process in which a cell acquires different sub-cellular structures to become a specialised cell.

Why is cell differentiation important?

It produces the different specialised cells the organism needs to form tissues and organs and carry out all its functions.

In mature animals, what is cell division mainly restricted to?

Repair and replacement of cells.

How do plant cells differ from most animal cells in their ability to differentiate?

Many plant cells keep the ability to differentiate throughout the plant's life, whereas most animal cells differentiate at an early stage and lose it.

True or false? Cell differentiation only happens while an organism is developing.

False. It also happens in mature organisms, producing specialised cells for repair and replacement.

What is the formula for magnification?

magnification = size of image $\div$ size of real object

What are the steps to find the real size of an object from a microscope image?
e.g. an image 50 mm long at magnification $\times 100$

1. Start from magnification = image size $\div$ real size
2. Rearrange: real size = image size $\div$ magnification
3. Divide: $50 \div 100 = 0.5$ mm

How does an electron microscope compare with a light microscope?

It has much higher magnification and resolving power, so cells can be studied in much finer detail and more sub-cellular structures can be seen.

What do the prefixes centi, milli, micro and nano mean?

$10^{-2}$, $10^{-3}$, $10^{-6}$ and $10^{-9}$ of the unit.
e.g. 1 nm $= 1 \times 10^{-9}$ m

How do you convert a length in millimetres into micrometres?
e.g. $0.05$ mm

1. 1 mm $= 1000\ \mu$m
2. Multiply by 1000: $0.05 \times 1000 = 50\ \mu$m

True or false? Ribosomes can be seen using a light microscope.

False. They are too small — an electron microscope is needed because of its higher resolving power.

What are the steps to prepare a slide of plant cells to view with a light microscope?
e.g. a piece of onion epidermis

1. Peel a thin layer and place it on a slide in a drop of water
2. Add a drop of iodine stain
3. Lower a cover slip at an angle with a mounted needle, then view using the lowest power objective first

Why is a stain such as iodine solution added when preparing a slide of cells?

To make the cells and their sub-cellular structures, such as the nucleus, visible.

Why is the cover slip lowered onto the specimen at an angle?

To prevent or reduce air bubbles under the cover slip.

Why must a thin layer of tissue be used on a microscope slide?

So light can pass through it and individual cells can be seen.

What must be included in a scientific drawing of cells seen under the microscope?

Clear continuous unshaded lines, labels of the cell parts, and a magnification or scale.

True or false? You should focus a light microscope using the highest power objective lens first.

False. Start with the lowest power objective to find and focus the cells, then move to a higher power.

How do bacteria multiply?

By simple cell division (binary fission), as often as once every 20 minutes given enough nutrients and a suitable temperature.

In what two ways can bacteria be grown in the laboratory?

In a nutrient broth solution, or as colonies on an agar gel plate.

What are the steps to calculate the number of bacteria after a given time from the mean division time?
e.g. 1 bacterium, mean division time 20 minutes, 60 minutes of growth

1. Number of divisions = time $\div$ division time: $60 \div 20 = 3$
2. Multiply the starting number by $2^{\text{number of divisions}}$: $1 \times 2^3 = 8$ bacteria

What are the steps to prepare an uncontaminated culture using aseptic technique?
e.g. inoculating an agar plate with bacteria

1. Sterilise the Petri dish and agar before use
2. Pass the inoculating loop through a flame, then spread the bacteria on the agar
3. Tape the lid on loosely, store the plate upside down and incubate at 25 °C

Why are cultures of microorganisms incubated at 25 °C in school laboratories?

At higher temperatures harmful pathogens are more likely to grow.

Why is the lid of a Petri dish secured with tape but not sealed all the way round?

The tape stops microorganisms in the air contaminating the culture, while air can still get in so harmful anaerobic bacteria do not grow.

What is a zone of inhibition?

The clear area around a disc on an agar plate where the bacteria have not grown.

How do you calculate the cross-sectional area of a zone of inhibition?
e.g. a clear zone of diameter 8 mm

1. Halve the diameter to get the radius: $8 \div 2 = 4$ mm
2. Use $\pi r^2$: $\pi \times 4^2 = 50.3$ mm$^2$

What does a larger zone of inhibition around a disc show?

That the antiseptic or antibiotic is more effective at killing or inhibiting the bacteria.

Why is a disc soaked in sterile water included on the agar plate?

As a control, to show that any zone of inhibition is caused by the antiseptic or antibiotic and not by the paper disc.

True or false? To use $\pi r^2$ for a zone of inhibition you must halve the measured diameter first.

True. The formula uses the radius, which is half the diameter.

Name two variables that must be kept the same when comparing different antiseptics using zones of inhibition.

e.g. the same bacterial culture and volume on each disc, and the same incubation temperature and time.

True or false? Every plant cell contains chloroplasts.

False. Only cells exposed to light, such as leaf mesophyll cells, have chloroplasts — root hair cells, for example, do not.

What is a plasmid?

A small ring of DNA in a bacterial cell, separate from the single DNA loop. A bacterium may have one or more.

True or false? The genetic material of a bacterial cell is enclosed in a nucleus.

False. It is a single loop of DNA free in the cytoplasm, not enclosed in a nucleus.