2: The Cell as the Basic Unit of Life Flashcards

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1
Q

What are the main inorganic chemical constituents of organisms?

A

Water and inorganic ions (mainly nitrate, magnesium, calcium, and iron).

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2
Q

What are the important functions of water?

A
  1. As a reactant: water takes part in some chemical reactions.
  2. As a medium for chemical reactions: It is also a good solvent that dissolves many substances. It provides an aqueous medium for chemical reactions to take place.
  3. As a medium of transport: substances dissolve in water and are carried around the body.
  4. As a cooling agent: water removes heat when it evaporates from the body of an organism, acting as a cooling agent.
  5. Provides support: water gives shape and provides support to organisms. It also provides buoyancy for aquatic plants and animals.
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3
Q

Which substances in humans are dissolved and transported in water?

A

Nutrients, waste, and gases dissolve in blood and are carried around the body. Meanwhile, blood contains about 90% water.

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4
Q

How do humans and plants cool down respectively?

A

Humans produce more sweat when the body temperature is high. Sweat mainly consists of water; its evaporation helps cool down the body.
Plants lose water in the form of water vapour to the atmosphere through transpiration. This helps take away heat away from the plants, preventing them from overheating.

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5
Q

How does water provide support to soft-bodied animals and plants respectively?

A

Some soft-bodied animals, like earthworms and jellyfish, have a fluid-filled cavity in their bodies. The hydrostatic pressure built up inside the body cavity gives support to the animals.
When plant cells are full of water, they become turgid and press against each other. This gives support to young seedlings so that the seedlings can stand upright.

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6
Q

What are the main functions of nitrate?

A

It is a source of nitrogen in plants for the synthesis of proteins. Animals obtain nitrogen through feeding on plants and other animals.

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7
Q

What are the main functions of magnesium?

A

It is a component of chlorophyll in plants. It also activates some enzymes that are needed for regulating some metabolic reactions.

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8
Q

What are the main functions of calcium?

A

It is the main component of bones and teeth. It is required in some processes like muscle contraction, blood clotting and sending messages in the nervous system. It also helps strengthen the cell wall in plants.

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9
Q

What are the main functions of iron?

A

It is a component of haemoglobin, which is an oxygen-carrying component in red blood cells. It also activates some enzymes.

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10
Q

What are the main organic chemical constituents of organisms?

A

Carbohydrates, lipids, proteins, and nucleic acids. They are often called biomolecules, and all contain carbon atoms.

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11
Q

What are the main functions of carbohydrates?

A

Carbohydrates contain carbon, hydrogen, and oxygen atoms. Glucose, starch, and cellulose are three common types of carbohydrates.
Glucose is directly broken down in respiration to release energy for body activities.
Starch acts as an energy reserve in plants. It is broken down to glucose to release energy when needed.
Cellulose is the main component of plant cell walls.

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12
Q

What are the main functions of lipids?

A

Lipids also contain carbon, hydrogen, and oxygen atoms, but they have a much greater hydrogen-to-oxygen ratio than carbohydrates. Triglycerides and phospholipids are two common types of lipids.
Triglycerides act as an energy reserve in our body. They also help reduce heat loss from the body by acting as a heat-insulating layer under the skin and protect the internal organs by cushioning them as a shock absorber.
Phospholipids are the main component of cell membranes.

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13
Q

What are the main functions of proteins?

A

Proteins contain carbon, hydrogen, oxygen, and nitrogen atoms, while some also contain sulphur atoms. Proteins make up many body tissues like hair, muscles, and skin.
Enzymes are proteins that can speed up (catalyse) reactions in our body.
Antibodies are proteins that are important in defending our body against diseases.

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14
Q

What are the main functions of nucleic acids?

A

Nucleic acids contain carbon, hydrogen, oxygen, nitrogen, and phosphorus atoms. There are two types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA carries genetic information that controls activities of the cells and determines the features organisms.
RNA is involved in the synthesis of proteins.

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15
Q

What is the discovery of cells?

A

In 1665, an English scientist Robert Hooke designed a microscope and used it to examine a thin slice of cork. He observed that cork seemed to be made up of many small irregular boxes. He called these boxes “cells”.

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16
Q

What is the Cell Theory?

A

The Cell Theory was proposed by Theodor Schwann. It (with modifications by other scientists) states that:
1. all organisms are made up of one or more cells
2. the cell is the basic unit of life, it is the smallest. until that shows all the characteristics of life
3. all cells come from pre-existing cells.

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17
Q

What are electron microscopes and two common types of electron microscopes?

A

Electron microscopes were invented in the 1930s. They use electron beams instead of light to form an image. They can produce images with higher magnifications and resolution, thus allowing scientists to study cells in greater detail. Two common types of electron microscopes are transmission electron microscopes and scanning electron microscopes.

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18
Q

What are the functions of transmission electron microscopes?

A

In a transmission electron microscope, electron beams pass through the specimen to form an image. They can be used to study the internal structures of a specimen. They produce two-dimensional, black-and-white images magnified up to 1.5 million times.

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19
Q

What are the functions of scanning electron microscopes?

A

In a scanning electron microscope, electron beams scan over the surface of the specimen. Scanning electron microscopes can be used to study the external structures of a specimen. They produce three-dimensional, black-and-white images magnified up to 300 000 times.

20
Q

What are objectives in a light microscope?

A

Objectives are magnifying lenses pointing to the specimen.

21
Q

What is the condenser in a light microscope?

A

The condenser is a lens to focus light onto the specimen.

22
Q

What is the nature of the image observed under a light microscope?

A

It is upside down and laterally inverted.

23
Q

How can we calculate the total magnification of a light microscope?

A

The total magnification of a light microscope is give by the product of eyepiece magnification and object magnification.

24
Q

How can we calculate the size of a cell under a light microscope?

A

If given the total magnification and the size of the image, the size of the cell is equal to the size of the image divided by the magnification.

25
Q

What are the characteristics of an image under a high-power magnification in a light microscope compared to that with a low-power magnification?

A

Compared with the observation at low-power magnification, the area of specimen observed under high-power magnification is smaller. More details of the specimen can be observed, and the image is dimmer.

26
Q

What is the structure of animal cells?

A

Animal cells share the same basic structure. The major part of the cell is a watery fluid called cytoplasm. The cytoplasm is bounded by a cell membrane. Various organelles, including the nucleus, rough endoplasmic reticulum, smooth endoplasmic reticulum, mitochondria, vacuoles, and ribosomes, are held in the cytoplasm.

27
Q

What are the features of the cell membrane?

A

It is a thin and flexible membrane. It encloses the cell and separates the cell contents from the outside environment.
It is differentially permeable (it only allows certain substances to pass through). It controls the movement of substances in and out of the cell.

28
Q

What are the features of cytoplasm?

A

It is a jelly-like fluid consisting of mainly water and proteins.
It holds many organelles like the nucleus and mitochondria.
It is the site for many chemical reactions.
It allows the movement and transport of materials inside the cell.

29
Q

What are the features of the nucleus?

A

It is a spherical structure bounded by a double membrane called the nuclear membrane . There are pores on the nuclear membrane, which allow certain substances to pass through.
It contains DNA, which carries genetic information that controls activities of the cell.

30
Q

What are the features of mitochondria?

A

They are rod-shaped structures bounded by a double membrane. The inner membrane is folded into finger-like projections.
They are the main site where the energy-releasing stage of respiration takes place.
They are abundant in cells that require a lot of energy.

31
Q

Give three examples of cells abundant in mitochondrion.

A
  1. Liver cells which have a high level of metabolic activities
  2. epithelial cells in the inner wall of the small intestine which needs energy for the absorption of nutrients
  3. enzyme-secreting cells which need energy for the synthesis of enzymes.
32
Q

What are the features of endoplasmic reticulum?

A

It is a network of interconnected membrane-bounded sacs.
It is continuous with the outer nuclear membrane and extends throughout the cytoplasm.
It provides a large surface area for the synthesis of lipids and proteins.
There are two types of ER, rough ER and smooth ER.

33
Q

What are the differences between rough endoplasmic reticulum and smooth endoplasmic reticulum?

A

Rough ER has ribosomes attached, but smooth ER does not.
Rough ER is involved in thee synthesis of proteins while smooth ER is involved in the synthesis of lipids.
Rough ER is abundant in cells that produce protein hormones or enzymes, while smooth ER is abundant in cells that produce lipid hormones.

34
Q

Give one example for cells abundant in rough and smooth endoplasmic reticulum respectively.

A

Rough ER: saliva-secreting cells
smooth ER: cells that secrete male sex hormones in testes

35
Q

What are the features of the vacuole in the animal cell?

A

Most animal cells have only a few small vacuoles or even no vacuole. It is a fluid-filled sac bounded by a single membrane. It contains water and dissolves substances such as food and enzymes.

36
Q

What are the similarities and differences between the structure of animal and plant cells?

A

Plant cells are generally larger than animal fells and they have a more regular shape. The basic structure of plants cells is similar to that of animal cells. They both have a cell membrane, cytoplasm, nucleus, mitochondria, and endoplasmic reticulum. In addition, plant cells have a cell wall and a large central vacuole. Some plant cells also have chloroplasts.

37
Q

What are the features of the cell wall?

A

It is a thick, rigid layer covering the cell membrane.
It is mainly made up of cellulose.
It is fully permeable; it allows water and all dissolved substances to pass through.
It protects, supports, and gives shape to the plant cell.

38
Q

What are the features of the vacuole in the plant cell?

A

Plant cells often have a large central vacuole.
It is filled with a fluid called cell sap. The cell sap contains water and dissolved substances such as glucose, pigments and waste.
When it is full of water, the cell becomes turgid. This provides support to the plant.

39
Q

What are the features of chloroplasts?

A

It is present in some plant cells only.
It is bounded by a double membrane.
It contains a green pigment called chlorophyll, which absorbs light energy for photosynthesis.

40
Q

Give two examples of plant cells containing chloroplasts.

A

Palisade mesophyll cells, guard cells

41
Q

What are the levels of body organisation in humans?

A

cell, tissue, organ, system, organism

42
Q

What is the meaning of a true nucleus?

A

The nucleus is surrounded by a nuclear membrane.

43
Q

What is the definition of eukaryotes?

A

Eukaryotes are organisms consisting of eukaryotic cells. Eukaryotic cells are cells with a true nucleus and genetic material (DNA) enclosed within the nucleus.

44
Q

What is the definition of prokaryotes?

A

Prokaryotes are organisms consisting of prokaryotic cells. Prokaryotic cells do not have a true nucleus, and have genetic material (DNA) lying free in the cytoplasm.

45
Q

What are the features of prokaryotic cells?

A

They do not have a true nucleus. Their genetic material (DNA) lie free in the cytoplasm.
Most of them have a cell wall; however, the cell wall does not contain cellulose.
They do not have endoplasmic reticulum. Ribosomes are lying free in the cytoplasm.
They do not have organelles bounded by a double membrane like mitochondria and chloroplasts.