Bk 1A Ch.2 Note

The two main groups of chemical constituents of organisms are inorganic and organic constituents.

The functions of water in organisms include:

1. As a reactant in some chemical reactions, e.g. photosynthesis
2. As a medium for chemical reactions
3. As a medium of transport to transport substances
4. As a cooling agent to remove heat through evaporation
5. Provides support and gives shape to organisms
6. As a component of lubricant to reduce friction during movement

Nitrate serves as a source of nitrogen for the synthesis of proteins in plants.

Magnesium activates some enzymes in animals.

Iron is a component of haemoglobin in red blood cells and activates some enzymes.

Calcium is a component of bones and teeth, and is needed for processes like blood clotting, muscle contraction, and sending messages in the nervous system.

Phosphate is a component of bones and teeth, and is also a component of phospholipids and nucleic acids.

Calcium helps strengthen cell walls in plants.

Magnesium is a component of chlorophyll and activates some enzymes in plants.

Phosphate is a component of phospholipids and nucleic acids in plants.

Nitrates provide the element nitrogen for the synthesis of proteins.

Magnesium is essential for forming chlorophyll in plants.

Calcium is important for:

1. Keeping bones and teeth strong
2. Blood clotting
3. Muscle contraction
4. Sending messages in the nervous system

The major organic chemical constituents of organisms that contain carbon are biomolecules, which include:

1. Making up body tissues
2. Regulating chemical reactions
3. Protecting the body against pathogens

Robert Hooke discovered cells in 1665 by examining a thin slice of cork. He observed that cork was made up of many small irregular boxes, which he named 'cells'. These were actually the cell walls of dead cork cells.

The Cell Theory 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 unit that shows all the characteristics of life.
3. All cells come from pre-existing cells.

Light passes through a specimen or a thin slide of it to form an image.

1600 times

Light microscopes produce colored images, while electron microscopes produce black and white images. Transmission electron microscopes show two-dimensional images of internal structures, and scanning electron microscopes show three-dimensional images of external structures.

Living specimens can be observed and specimens can be prepared easily.

1,500,000 times

200,000 times

Electron beam passes through a very thin slide of a specimen to form an image, or electron beams scan over the surface of a specimen to form an image.

The higher the resolution of an electron microscope, the clearer the image produced and the more details it shows.

The two sets of lenses in a light microscope are the eyepiece and the objective.

The eyepiece is a magnifying lens through which our eyes look to view the specimen.

The body tube holds the eyepiece and the objectives in place.

The nosepiece allows us to rotate and choose the required objective lens.

The condenser is a lens that focuses light onto the specimen.

The diaphragm controls the amount of light that is shone onto the specimen.

The objective lens is a magnifying lens that points directly to the specimen.

The light source provides light for viewing the specimen.

The arm is used to hold the microscope for carrying it from place to place.

The coarse adjustment knob is used for rough focus and causes a larger movement of the stage, while the fine adjustment knob is used for sharp focus and causes a smaller movement of the stage.

Light from the light source penetrates the specimen, enters the objective, passes through the eyepiece, and finally enters our eye, resulting in an inverted image.

The stage is where the slide is clipped for observation and can be raised or lowered to focus.

The base supports the whole microscope.

Magnification represents how many times an image is larger than the object.

Total magnification is calculated by multiplying the magnification of the eyepiece by the magnification of the objective.

At low-power magnification, a larger area of the specimen is observed, allowing more cells to be seen. In contrast, at high-power magnification, a smaller area is observed, resulting in fewer cells being visible.

Low-power magnification shows fewer details of the specimen, while high-power magnification reveals more details.

Low-power magnification results in a brighter image, whereas high-power magnification produces a dimmer image.

The magnification is calculated as follows: 10X (eyepiece) x 10X (objective) = 100X.

To calculate the average actual width of an onion epidermal cell, use the formula:

Actual length = (Image length / Magnification)

Given that the image length (MN) is 0.06 cm and the magnification is 100X, the calculation is:

Actual length = 0.06 cm / 100 = 0.0006 cm = 6 um.

The image observed with a 40X objective will appear larger and more detailed compared to the image observed with a 10X objective. However, the field of view will be smaller, meaning less of the sample will be visible at one time.

• Size: Plant cells are generally larger than animal cells.
• Shape: Plant cells have a more regular shape compared to animal cells.
• Cell Wall: Plant cells possess a cell wall, while animal cells do not.
• Organelles: Some plant cells contain a large central vacuole and chloroplasts.

The nucleus is spherical, bounded by the nuclear membrane, contains the genetic material (DNA), and controls the activities of the cell.

The cytoplasm is a jelly-like fluid mainly consisting of water and protein.

The cell membrane holds organelles, provides a site for chemical reactions, allows movement and transport of materials, is thin and flexible (mainly made of phospholipids and proteins), encloses the cell, is differentially permeable, and controls the movement of substances into and out of the cell.

The cell wall is a thick, rigid outermost layer mainly made up of cellulose. It is differentially permeable and protects, supports, and gives shape to the plant cell.

The two types of ER are:

1. Rough ER: Has ribosomes attached and is involved in the synthesis of protein; abundant in cells that produce a large amount of proteins.
2. Smooth ER: Lacks ribosomes and is involved in the synthesis of lipid; abundant in cells that produce a large amount of lipids.

Ribosomes are involved in the synthesis of proteins and can be found either attached to the rough endoplasmic reticulum (ER) or free in the cytoplasm.

The mitochondrion is the main site of respiration, which releases energy. It is abundant in cells that use a lot of energy and is bounded by a double membrane with the inner membrane being highly folded.

Chloroplasts contain chlorophyll, a green pigment that captures light energy for photosynthesis. They are bounded by a double membrane and often contain starch grains.

Vacuoles are often large in plant cells, providing turgidity and support when full of water, while they are small or absent in animal cells.

The features that can help determine if a cell is an animal cell or a plant cell include:

1. Absence of cell wall - Animal cells do not have a cell wall, while plant cells do.
2. Presence of chloroplasts - Chloroplasts are present in plant cells for photosynthesis, but absent in animal cells.
3. Presence of nucleus - Both animal and plant cells have a nucleus, so this feature does not help in distinguishing between them.

The purpose of staining with iodine solution is to give color to cell structures for easier observation. This enhances visibility under the microscope.

The function of the rough endoplasmic reticulum is to synthesize and transport proteins within the cell. It is studded with ribosomes, which give it a 'rough' appearance.

The function of the nucleus is to store genetic material (DNA) and control the cell's activities, including growth, metabolism, and reproduction.

The function of chloroplasts is to conduct photosynthesis, converting light energy into chemical energy stored in glucose, and they contain chlorophyll, which captures light energy.

The function of mitochondria is to produce energy (ATP) through cellular respiration, serving as the powerhouse of the cell.

The function of the vacuole is to store water and dissolved substances, helping to maintain turgor pressure and support the cell structure.

Mitochondria are too small to be seen under a light microscope.

1. Chloroplasts carry out photosynthesis to produce glucose.
2. Mitochondria then use this glucose to perform respiration, releasing energy for the cell's functions.

Eukaryotic cells are defined by the presence of a true nucleus surrounded by a nuclear membrane and various membrane-bound organelles. Examples include plant cells and animal cells.

Prokaryotic cells are defined as cells that do not have a true nucleus. An example of prokaryotic cells is bacterial cells.

Organisms consisting of eukaryotic cells are called eukaryotes (真核生物).

Organisms consisting of prokaryotic cells are called prokaryotes (原核生物).

The most reasonable sequence is C: (3), (1), (2), (5), (6). This involves searching the field with the 10X objective, focusing with the 10X objective, then the 40X objective, moving the slide to center the protist, and finally turning on the light when necessary.

The observable structure in the study would be B: chloroplast, as it is a key component of photosynthesizing protists.

The cell is the basic unit of organisms.

Tissues are formed when similar cells work together for one or more particular functions.

Organs are made up of different tissues that work together for one or more particular functions.

Systems consist of different organs that work together to perform a particular task.

The highest level of body organization is the organism, where different systems work together to maintain life.