2.1 Organisms Questions and Answers

2.1 Organisms – Questions and answers

Q1.

Bk Ch2 S2.1 Q1

Describe the cell theory that is accepted by scientists today.

A1.

Bk Ch2 S2.1 A1

The cell theory states that cells are the smallest units of life, that all living things are made up of cells and that all cells come from pre-existing cells.

Q2.

Bk Ch2 S2.1 Q2

Outline the historical development of the cell theory. Include a discussion of the contributions or evidence of Robert Hooke and Anton van Leeuwenhoek.

A2.

Bk Ch2 S2.1 A2

The invention of the light microscope was critical in the development of our understanding of cells. Before this no-one could actually see cells. In 1665 Robert Hooke was the first person to use a microscope to observe and describe the cells of cork. In 1676 Anton van Leeuwenhoek observed unicellular organisms in stagnant water, describing them as ‘animalcules’. By the 19th century microscopes were advanced enough to allow cells to be viewed in some detail. In 1831 Robert Brown described the nucleus of cells, stating that the nucleus was present in plant and animal cells. All of these developments supported the idea that living things are made of cells. By the late 19th century scientists were able to observe cell division occurring in the cells of stained, living tissue using the microscope. In the 19th century Louis Pasteur disproved the theory of ‘spontaneous generation’ when his experiments showed that micro-organisms arose only from other micro-organisms.

Q3.

Bk Ch2 S2.1 Q3

Prepare a point-form summary comparing the light and electron microscopes. Include an explanation of how the respective microscopes operate, their magnifying powers, resolution and applications.

A3.

Bk Ch2 S2.1 A3

Light microscope / Electron microscope
A beam of light passes through the specimen, through the objective lens and up the barrel of the microscope, through the ocular lens (eyepiece), then reaches the eye of the observer / Uses a beam of electrons to produce an image of the item being observed
Can magnify objects up to about 1500 times / Can magnify objects up to 1 000 000 times
Resolving power of up to 0.2 mm (about 500 times the ability of the human eye) / Resolving power of about 0.0002 mm (about five million times the ability of the human eye)
Used to observe general features of microscopic objects such as cells / Used to illustrate the internal structure of cells and cellular organelles and produce images of the surfaces of microscopic objects

Q4.

Bk Ch2 S2.1 Q4

Prepare a table that summarises the cell structures visible using these two different kinds of microscope.

A4.

Bk Ch2 S2.1 4

Cell structure / Structure visible using
Light microscope / Electron microscope
Cell membrane / ü (if stained) / ü
Nucleus / ü / ü
Mitochondria / ü (but not in detail) / ü
Ribosomes / x / ü
Golgi body / x / ü
Vacuole / ü / ü
Cell wall / ü / ü
Chloroplast / ü / ü
Lysosomes / x / ü
Endoplasmic reticulum / x / ü
Microtubules / x / ü

Q5.

Bk Ch2 S2.1 Q5

a Identify the structures indicated on the diagram of the cell shown.

b Describe the function of each of the organelles you have identified in (a).

A5.

Bk Ch2 S2.1 A5

a W: nucleus; X: cytoplasm; Y: cell membrane; Z: mitochondrion.

b The nucleus contains the chromosomes; it controls the development and activities of the cell. The cytoplasm is the site of most cell activities; it contains the organelles, each of which has a specific function. The cell membrane is the boundary between the cell’s cytoplasm and the external environment of the cell; the cell membrane controls the movement of materials into and out of cells. The mitochondria are organelles that are involved in the energy transformations within cells and are the site of cellular respiration.

Q6.

Bk Ch2 S2.1 Q6

Study the following electron micrographs.

X / Y / Z

a Name each of the organelles X, Y and Z.

b Describe the function of each organelle.

Comment on the relationship between the structural features shown and the function you have stated.

A6.

Bk Ch2 S2.1 A6

a X: nucleus; Y: mitochondrion; Z: Golgi body.

b The nucleus is the control centre of the cell. It regulates the development of the cell and all of the cell activities. The large pores evident on the surface of the nucleus allow molecules to enter and leave the nucleus.

Mitochondria are the site of energy transformations within cells. This is where the chemical reactions of cellular respiration occur. The inner walls of the mitochondria, where the chemical reactions occur, are greatly folded, increasing the internal surface area and therefore maximising the space for chemical reactions to occur.

The Golgi body is important because this is where proteins and some other substances are finally processed before secretion from the cell and sometimes into the cell. The flattened shape of the membrane sacs increases the efficiency of exchange of materials between the Golgi complex and the surrounding fluid.

Q7.

Bk Ch2 S2.1 Q7

Match the term listed in the left column with its correct description or role in the right column.

organelle dark-staining area within nucleus

protoplasm membrane-bound sac within cytoplasm, may contain dissolved nutrients or wastes for storage

cell wall small spherical body; site of protein production

nucleolus sub-cellular structure with a particular function

vacuole rigid cellulose structure surrounding plant cells that provide support for cells

chloroplast contents of cell

ribosome stack of flattened membrane sacs that stores and distributes substances within cell and secretes substances out of cell

Golgi body green plastid found in plant cells; site of photosynthesis

A7.

Bk Ch2 S2.1 A7

organelle sub-cellular structure with a particular function

protoplasm contents of cell

cell wall rigid cellulose structure surrounding plant cells that provide support for cells

nucleolus dark-staining area within nucleus

vacuole membrane-bound sac within cytoplasm, may contain dissolved nutrients or wastes for storage

chloroplast green plastid found in plant cells; site of photosynthesis

ribosome small spherical body; site of protein production

Golgi body stack of flattened membrane sacs that stores and distributes substances within cell and secretes substances out of cell

2.1 Cell theory QA page 1 of 3