Question 1

The 'Cell theory' states that all living things are made of cells.Which of the statements below also form part of the 'cell theory'?

Accepted Answer

The cell theory states that all biological organisms are composed of cells; cells are the unit of life and all life come from preexisting life.

Question 2

Some people say that the cell theory isn't a good theory because there are exceptions.Which of the following could be considered an exception to cell theory?

Accepted Answer

The cell theory states that all biological organisms are composed of cells; cells are the unit of life and all life come from preexisting life. However, there are exceptions/discrepancies to the cell theory-1) skeletal muscle is composed of muscle fibres, these are long fibres that can measure 300mm or more and are therefore much larger than regular cells. In addition to this, each muscle fibre contains multiple nuclei.2) Giant algae: these organisms are able to grow up to 100 mm in length yet they are unicellular and contain only one nucleus.

Question 3

There are seven processes which are said to be possessed by all living things.This venus fly trap has just caught an unfortunate fly. The fly is trying to escape from the trap.,Which characteristic of living things, shared by both plants and insects, is illustrated by the action in this photo?

Accepted Answer

The characteristics of living things are - metabolism, response, homeostasis, growth, reproduction, excretion & nutrition.Here, the fly is responding to the closing trap, and the trap has responded to the presence of the fly.Thus, option D is correct.

Question 4

Which ratio is thought to limit the size of cells?

Accepted Answer

Cell size is limited by the surface area to volume ratio of the cell. As the volume of a cell increases, it becomes harder to efficiently transport materials in and out of the cell.

Question 5

A single stem cell can form a range of different daughter cells. Which of the statements best describes how this happens?

Accepted Answer

Stem cells are different from other cells in the body in three ways: They can divide and renew themselves over a long time. They are unspecialized, so they cannot do specific functions in the body. They have the potential to become specialized cells. By controlling the expression of genes, stem cells differentiate into different type of cells such as muscle cells, blood cells, and brain cells.

Question 6

Which of the following are special properties of stem cells which make them so useful for new medical treatments?

Accepted Answer

Stem cells are different from other cells in the body in three ways: They can divide and renew themselves over a long time. They are unspecialized, so they cannot do specific functions in the body. They have the potential to become specialized cells. By controlling the expression of genes, stem cells differentiate into different type of cells such as muscle cells, blood cells, and brain cells. This property make them so useful for new medical treatments.

Question 7

The electron microscope image below shows a scale bar marked with 10μm.It has been measured to be 3.5 cm (i.e. 35 mm ) long by a student using the rule shown.What is the magnification of this image?

Accepted Answer

1 µm = 0.001 mm So, 10 µm = 0.01 mmMagnification = image size / actual size =0.0135​So, magnification is ×3500.

Question 8

The erythrocytes below were imaged using an electron microscope.The magnification is ×3000 and the ruler measures the central cell as being 2 cm in diameter.Estimate the actual size of this erythrocyte.

Accepted Answer

1 cm = 10000 µm So, 2 cm = 20000 µmMagnification = image size / actual size Actual size can be calculated as, 300020000​=6.6 µm

Question 9

Which of the following options is not a source of stem cells?

Accepted Answer

A, B and C can all contain stem cells but at different levels of specialisation. Embryonic stem cells can differentiate into any type of cell (totipotent), umbilical cord stem cells can differentiate into a narrower range of cells (pluripotent), and bone marrow stem cells can only differentiate into a narrow range of different types of cells (multipotent).

Question 10

The electron micrograph below shows a plant cell.The scale bar (measuring 45 mm in length) on this drawing represents a length of 10 μm.Which of the following correctly represents the magnification of the electron micrograph?

Accepted Answer

1 µm = 0.001 mm So, 10 µm = 0.01 mmMagnification = image size / actual size =0.0145​So, magnification is ×4500.

Question 11

What provides evidence for the endosymbiotic theory?

Accepted Answer

An endosymbiont is one organism that lives inside of another one. All eukaryotic cells, like your own, are creatures that are made up of the parts of other creatures. During the 1950s and 60s, scientists found that both mitochondria and plastids inside plant cells had their own DNA. It was different from the rest of the plant cell DNA. When scientists looked closer at the genes in the mitochondrial and plastid DNA, they found that the genes were more like those from prokaryotes. This tells us that organelles are more closely related to prokaryotes.

Question 12

Which characteristic of stem cells makes them useful for treating Stargardt's disease?

Accepted Answer

Stargardt's Disease is the most common form of inherited macular degeneration. The progressive vision loss associated with Stargardt's disease is caused by the degeneration of photoreceptor cells in the central portion of the retina called the macula. Stem cells can differentiate into retinal cells and thus serve as an important tool for treating Stargardt's disease.

Question 13

The diagram shows a heterotrophic, unicellular, freshwater organism that has been placed in distilled water. The short arrows show movement of water and the long arrows show a sequence of steps.What life function is illustrated?

Accepted Answer

Homeostasis is any self-regulating process by which an organism tends to maintain stability while adjusting to conditions that are best for its survival. In the given figure, the cell is trying to maintain its osmotic balance by osmoregulation. The body cells does not exist in isolation. There is a constant input of water and electrolytes into the system. Excess water, electrolytes, and wastes are transported out of the cell.

Question 14

What is a function of the plant cell wall?

Accepted Answer

Cells with a cell wall will swell when placed in a hypotonic solution, but once the cell is turgid (firm), the tough cell wall prevents any more water from entering the cell.  Thus, cell wall can withstand dilute hypotonic media and prevents bursting of cells.  For example, cell walls of desiccation tolerant resurrection plants withstand extreme mechanical stress during complete dehydration and rehydration.

Question 15

In mammals, mature red blood cells are specialized in that they lack nuclei, mitochondria or ribosomes. Which statement applies to red blood cells?

Accepted Answer

Because of the lack of nuclei and mitochondria, mature red blood cells are incapable of generating energy via the (oxidative) Krebs cycle.

Question 16

What distinguishes prokaryotic cells from eukaryotic cells?

Accepted Answer

Both prokaryotic cells and eukaryotic cells possess plasma membrane and cellular organelles. Eukaryotic mitochondria and chloroplast possess 70S ribosomes similar to prokaryotes. However, the cytosolic ribosome of eukaryotes is 80S type. Prokaryotic cells have no internal membrane-bound organelles within their cytoplasm.

Question 17

What is an example of binary fission?

Accepted Answer

Binary fission is similar in concept to the mitosis that happens in multicellular organisms (such as plants and animals), but its purpose is different.When cells divide by mitosis in the body of a multicellular organism, they cause the organism to grow larger or replace old, worn-out cells with new ones. In the case of a bacterium, however, cell division isn’t just a means of making more cells for the body. Instead, it’s actually how bacteria reproduce, or add more bacteria to the population.

Question 18

Where are proteins synthesized by free ribosomes used?

Accepted Answer

In mammalian cells, the initial sorting of proteins to the ER takes place while translation is in progress. Most proteins synthesized on free ribosomes remain in the cytosol or are transported to the nucleus, mitochondria, chloroplasts, or peroxisomes. In contrast, proteins synthesized on membrane-bound ribosomes are translocated into the ER while their translation is in progress. They may be either retained within the ER or transported to the Golgi apparatus and, from there, to lysosomes, the plasma membrane, or the cell exterior via secretory vesicles.

Question 19

The diagram shows a prokaryotic cell.What are the structures labelled Y and Z ?

Accepted Answer

The nucleoid, labelled Y (meaning nucleus-like) is an irregularly shaped region within the prokaryotic cell that contains all or most of the genetic material.Ribosomes are sites for protein synthesis. They are of two types 70S and 80S. Prokaryotes have 70S type ribosomes, labelled Z.

Question 20

What is the structure labeled X in the electron micrograph of a rat liver cell?

Accepted Answer

The given electron micrograph of a rat liver cell shows mitochondria, labelled X. Although the shape is sigmoid, slightly different from classic ovoid, but the membrane infoldings known as cristae are clearly visible.

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