Cell Structure Flashcards

All 46 cards in this deck

What is a eukaryotic cell?

A cell whose genetic material (DNA) is enclosed in a nucleus, and which has membrane-bound organelles.

Name three types of organism made of eukaryotic cells.

Animals, plants and fungi (also protists).

What is the function of the nucleus?

Contains the genetic material (DNA) and controls the activities of the cell.

What is the function of ribosomes?

The site of protein synthesis.

What is the function of mitochondria?

The site of aerobic respiration, which releases energy for the cell.

True or false? A very active cell, such as a muscle cell, contains many mitochondria.

True. More mitochondria means more aerobic respiration, releasing more energy.

Which three sub-cellular structures are found in plant cells but not in animal cells?

Cell wall, chloroplasts and a large (permanent) vacuole.

What is the function of the cell wall in a plant cell?

Made of cellulose; it strengthens and supports the cell.

What is the function of a chloroplast?

Contains chlorophyll, which absorbs light so photosynthesis can take place.

What is the function of the permanent vacuole in a plant cell?

Contains cell sap and keeps the cell turgid, helping support the plant.

What is the function of the cell membrane?

Controls which substances enter and leave the cell.

True or false? Every cell in a plant contains chloroplasts.

False. Only cells that photosynthesise have them; underground cells such as root or potato tuber cells do not.

What is a prokaryotic cell?

A cell with no nucleus — its genetic material is a single loop of chromosomal DNA free in the cytoplasm.

What is plasmid DNA?

Small rings of extra DNA in a bacterial cell, separate from the chromosomal DNA.

What is the function of a flagellum in a bacterium?

A long whip-like tail that rotates to move the bacterium (makes it motile).

Which sub-cellular structures do bacterial cells share with animal cells?

Cell membrane, cytoplasm and ribosomes.

True or false? Bacteria do not have ribosomes.

False. Bacteria do have ribosomes (smaller than those in eukaryotes) for making proteins.

How does the size of a bacterial cell compare with that of an animal cell?

Much smaller — bacteria are about $1\ \mu\text{m}$ across, animal cells about $10$–$100\ \mu\text{m}$.

What is the function of the acrosome in a sperm cell?

Contains digestive enzymes that break down the outer layers of the egg cell so the sperm can enter.

Why does a sperm cell contain many mitochondria?

To release energy by respiration so the tail can beat and the sperm can swim to the egg.

Why do sperm cells and egg cells have a haploid nucleus?

Each has only half the number of chromosomes, so fertilisation restores the full number in the zygote.

What happens to the egg cell membrane immediately after fertilisation?

It changes so that no more sperm can enter the egg.

Why does the cytoplasm of an egg cell contain nutrients?

To supply the developing embryo with food (energy) after fertilisation.

How is a ciliated epithelial cell adapted to its function in the airways?

It has cilia on its surface that beat to waft mucus (with trapped dust and bacteria) away from the lungs.

What is the magnification equation?

$\text{magnification} = \dfrac{\text{image size}}{\text{actual size}}$

What are the steps to find the actual size of a cell from a microscope image?

e.g. image width $8\ \text{mm}$, magnification $\times 400$

1. Rearrange: actual size = image size ÷ magnification
2. Divide: $8 \div 400 = 0.02\ \text{mm}$
3. Convert if asked: $0.02\ \text{mm} = 20\ \mu\text{m}$

What are the steps to work out the total magnification of a light microscope?

e.g. a $\times 10$ eyepiece lens with a $\times 40$ objective lens

1. Read the eyepiece lens power: $\times 10$
2. Read the objective lens power: $\times 40$
3. Multiply them: $10 \times 40 = \times 400$

What is meant by the resolution of a microscope?

The shortest distance between two points that can still be seen as two separate points.

Give one advantage of an electron microscope over a light microscope.

It has much higher magnification and resolution, so structures are seen in far greater detail.

Name two sub-cellular structures that can only be seen using an electron microscope.

Ribosomes and plasmids (also the internal structure of mitochondria and chloroplasts).

What are the steps to prepare a slide of a thin plant specimen for a light microscope?

e.g. a peel from a leaf

1. Place the thin peel flat on a slide in a drop of water.
2. Add a drop of stain such as iodine.
3. Lower a coverslip at an angle with a mounted needle to avoid air bubbles.

State two reasons for placing a coverslip on top of a specimen.

To keep the specimen flat and in place, and to protect the specimen and the objective lens.

Why must a specimen such as a leaf peel be thin?

So light can pass through it, allowing the cells to be seen.

Why is a stain such as iodine added to a specimen on a slide?

It increases contrast so sub-cellular structures show up more clearly.

Which objective lens should you start with when focusing a light microscope, and which focusing knob is used last?

Start with the lowest power objective lens; use the coarse focus first, then the fine focus.

What should a labelled scientific drawing of a microscope specimen include?

A title, clear unbroken pencil lines with no shading, straight label lines that do not cross, and the magnification used.

True or false? A scientific drawing of cells should be shaded to show colour.

False. Scientific drawings use clear, unshaded pencil lines with labels.

What does the prefix milli mean?

One thousandth, $10^{-3}$; e.g. $1\ \text{mm} = 10^{-3}\ \text{m}$.

What does the prefix micro ($\mu$) mean?

One millionth, $10^{-6}$; e.g. $1\ \mu\text{m} = 10^{-6}\ \text{m}$.

What do the prefixes nano and pico mean?

Nano $= 10^{-9}$ and pico $= 10^{-12}$.

What is standard form?

A number written as $A \times 10^{n}$, where $1 \le A < 10$; e.g. $0.0077 = 7.7 \times 10^{-3}$.

What are the steps to convert a length in millimetres into micrometres?

e.g. $0.05\ \text{mm}$

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

When is it appropriate to use an estimate of size or number?

When an exact measurement is not possible or not needed — e.g. estimating cell numbers in a field of view, or checking a calculated answer is sensible.

True or false? A bacterial cell keeps its chromosomal DNA inside a nucleus.

False. Bacteria have no nucleus \u2013 the chromosomal DNA is a single loop free in the cytoplasm.

True or false? The tail of a sperm cell releases the energy the sperm needs to swim.

False. The tail propels the cell; the energy is released by the many mitochondria.

True or false? $1\ \mu\text{m} = 1000\ \text{nm}$.

True. A micrometre is $10^{-6}\ \text{m}$ and a nanometre is $10^{-9}\ \text{m}$.