Science Review Questions
1. The cell theory is a major theory of living things. The four statements are: 1. all living things are composed of one or more
cells. 2. Cells are the basic unit of structure and function in all organisms. 3. All cells come from previously existing cells. 4.
The activity of an entire organism depends on the total activity of its independent cells.
2. An organelle is a specialized structure that performs a specific function in the cell.
3. Scientists studying the cell have removed and replaced several of the cells organelles to study the function of the nucleus.
This showed these scientists that nucleus is the control centre of the cell.
A cell can perform all of its functions only when the nucleus is present and in good form. The nucleus coordinates controls
and manages all cell functions. It is the storage centre for all information and instructions for the organelles.
4. A gene is a segment of DNA on a chromosome determines a specific characteristic of an individual. A chromosome is a
double stranded, threadlike structure that carries genetic material (instructions for producing new cells with the same
characteristics as the parent cell)
5. The differences between and animal and plant cell are that the plant cell has a very rigid cell wall that lies outside of the
cell membrane. Plant cells contain chloroplasts, organelles that allow them to make their own food through a process known
as photosynthesis.
6. The stage between cell division is called interphase. During interphase, the cell takes in nutrients, such as sugars, and
builds protein. These are used by the cells for energy, growth and repair of damaged parts. Interphase allows for the cell to
grow and duplicate its genetic material. Before mitosis is complete, the cell must separate and half the cytoplasm and the
organelles empty into each cell. This process is called cytokinesis.
7. Before mitosis can begin, the nucleus must make a copy of its chromatin so that there are two complete sets of DNA. This
is known as replication. The replicated chromatin coils up to form double stranded chromosomes, which are joined at the
centre by a centromere. Two complete sets of DNA are bundled together as double stranded chromosomes.
8. Prophase: Spindle fibers form and stretch across the cell from centrioles. The chromosomes are thick and dense. Spindle
fibers attach to the centromeres. Metaphase: The tugging of the spindle fibers pulls the chromosomes into a line across the
middle of the cell. Anaphase: The spindle fibers contract and shorten, pulling apart the centromere. One strand of the
chromosome moves to opposite poles of the cell. Telophase: One complete set of chromosomes is at each pole of the cell.
Spindle fibers start to disappear and nuclear membranes form around each set of chromosomes. There are two nuclei and
the cell is now ready to divide.
9. Regeneration is the repair of injured cells or the making of lost body parts. When cells divide uncontrollably, this causes
cancer. Cancerous cells disrupt the normal function of the cells around it. They continue dividing and pile up one on top of
another. This causes a tumor or lump to form. These cells gobble up the oxygen of other cells and rob them of the food and
nutrients. The aging process occurs when the cells enter a state where they no longer divide or where mitosis slows and
stops. They believe that aging cells cannot repair themselves as well and cannot carry out their function.
10. Cells die because some cells are pre-programmed to die at a certain time in their life cycle. The genetics of the cell
decide this. Some cells die because there is something wrong with their makeup, usually with the nucleus of the cell.
11. Binary fission is an asexual process where a parent cell divides so that each new cell contains a single chromosome
carrying a complete set of DNA identical to the parent. E.g. Bacteria
Asexual reproduction is the formation of a new individual that has identical genetic information to the parent. Fragmentation
is when a small piece or fragment breaks away from the main mass and grows into a new organism. E.g hyphae. Budding is
the process where a bud grows on the cell wall, breaks off and forms a new individual. E.g sponges, hydras.