1 1 cell structure

A eukaryotic organism is an organism whose cells contain membrane-bound organelles, e.g. a nucleus and mitochondria.

False. Prokaryotic organisms do not contain a nucleus.

A prokaryotic organism is an organism whose cells lack a nucleus and other membrane-bound organelles.

True. Prokaryotic organisms are always single-celled.

A plasmid is a small circular loop of DNA found in prokaryotic cells.

True Eukaryotic cells are larger than prokaryotic cells. Eukaryotic cells are typically between 10 and 100 µm. Prokaryotic cells are much smaller in comparison to eukaryotic cells, with many measuring ~ 1 µm in size.

There are 1000 µm in 1 mm

1,000,000 in standard form is 1 x 106

False To convert a measurement from nanometres to micrometres you must divide by 1000

The eukaryotic cell is 2 orders of magnitude wider than the prokaryotic cell 1 = 100 and 100 = 102, therefore it is 2 orders of magnitude wider Be careful to check the units when comparing two numbers

The cell membrane separates cells from their surrounding environment.

The largest organelle within animal cells is the nucleus.

Plant cells have the following structures that are not present in animal cells:

True. Ribosomes are present in plant and animal cells. They are the site of protein synthesis.

Organelles present within animal cells are: Note that structures such as the cell membrane and cytoplasm are not organelles, so are not acceptable answers here.

Ribosomes are the smallest organelle; they are present in both plant and animal cells.

False. The gel-like fluid present in plant and animal cells is the cytoplasm. Chloroplasts are organelles found in plant cells.

False. The role of the nucleus is to store genetic information in the form of DNA. Energy is released by the mitochondria.

Chloroplasts absorb light energy during the process of photosynthesis.

False. Plant cell walls provide strength and additional structural support for plant cells. It is the membrane that regulates the passage of substances.

The permanent vacuole stores cell sap and provides structural support for plant cells.

True. Mitochondria are responsible for releasing energy through the process of aerobic respiration.

Specialised cells are cells that have developed specific characteristics that allow them to perform particular functions.

Examples of specialised plant cells include:

Examples of specialised animal cells include: You specifically need to know sperm cells, nerve cell and muscle cells

True. Root hair cells have an increased surface area to allow increased absorption of water and mineral ions from the soil.

The function of a nerve cell is to conduct electrical impulses and send signals around the body.

True. Muscle cells contain a lot of mitochondria to carry out aerobic respiration and provide energy for muscle contraction.

False. Sperm cells contain half the amount of DNA contained to normal body cells.

Root hair cells contain a lot of mitochondria to provide energy for the active transport of mineral ions from the soil into the cell.

Phloem cells form a long vessel to allow the plant to transport dissolved sugars and amino acids.

False. Xylem vessels are supported by lignin.

Cell differentiation is the process by which a cell changes to become specialised.

False. Almost all cells in a multicellular organism contain the same genetic information.

The features of specialised cells are determined by the expression of genes in the nucleus.

False. Many types of plant cells retain the ability to differentiate throughout life.

In animals most cell differentiation take place during the early stages of development when the animal is an embryo/fetus (before it is born).

A light microscope is an instrument that uses light and lenses to magnify specimens, allowing visualisation of cells and large subcellular structures.

Resolution in microscopy means the ability to distinguish between two closely spaced objects as separate entities.

An electron microscope is an instrument that uses electron beams instead of light to provide much higher resolution and magnification than light microscopes.

False. Electron microscopes use electron beams for imaging.

False. The first light microscopes to be invented allowed only very basic details of cell structure to be observed, such as cell shape and the plant cell walls.

The formula for calculating magnification is: magnification = image size ÷ actual size

False. Magnification does not have any units and is just written as, e.g. x10 or 5000x.

The equation for calculating the actual size of a specimen is: actual size = image size ÷ magnification

A magnification scale is included to show the actual size of the observed specimen.

A microscope slide is a thin, flat piece of glass on which specimens are prepared for observation under a microscope.

Methylene blue is used to stain cheek cells.

True. Iodine is used to stain onion cells.

Smudging the glass slide and trapping air bubbles under the coverslip should be avoided when preparing a microscope slide.

An objective lens is the lens on a microscope that is closest to the specimen. Most light microscopes have several objective lenses at different powers for viewing specimens at different levels of magnification.

False. When viewing a specimen under a light microscope the low-power lens should always be used first.

Biological drawings should follow specific rules, e.g.:

Biological drawings should take up at least half of the space available on the page

Binary fission is a type of simple cell division by which bacteria multiply.

The number of bacterial cells increases by a power of 2 (doubles) each time binary fission occurs.

Aseptic technique is a method used to prevent contamination by unwanted microorganisms when working with cultures.

False. ** Lifting the lid of a petri dish only slightly primarily reduces the risk of contamination by other microorganisms**.

The inoculating loop should be passed through a hot flame to kill any microorganisms present on the loop; this prevents contamination.

The lid should be secured with tape at intervals, rather than all the way around, to ensure that oxygen can enter the dish; this prevents the growth of anaerobic bacteria which may be harmful.

The maximum allowed temperature for growing bacteria in a school lab is 25°C. This is to restrict the growth of harmful pathogens.

An inhibition zone is an area around a disc of antibiotic, antiseptic, or disinfectant where bacterial growth is inhibited.

The equation for calculating the area of an inhibition zone is: Area of inhibition zone = πr2 Where π = 3.14 and r = the radius of the zone of inhibition

Mean division time is the average length of time that it takes for a bacterial cell in a population to divide.

True. The bigger the zone of inhibition, the more effective the antibiotic is at killing the bacteria.

If there is no zone of inhibition it indicates that the bacteria is resistant to a particular antibiotic.

When investigating the effect of antibiotics on bacterial growth using agar plates and zones of inhibition the control should be paper discs soaked in sterile water.

Bacteria can be cultured in a nutrient broth solution or as colonies on an agar gel plate.