Chapter 1: Cell structure and organisation 🧫

Question 1

What is a cell?

Answer 1

• A cell is a basic unit of life as it is the simplest unit of life, which makes up a living thing (an organism).
• A cell also requires air, water, and food to survive and live for a longer period of time.
• Cells also take in raw materials, which include undigested food molecules, they break them down and digest them to make new molecules. The cells either use these molecules or transport them to other body parts.
• Most cells are too small to be seen with the naked eye. Hence, the light and electron microscopes allow us to see cells and their parts at a much closer view.

Question 2

What is a light microscope?

Answer 2

• A light microscope can magnify an object up to 1000 times its original size.
• It produces coloured light micrographs (diagrams/pictures).

Question 3

What is an electron microscope?

Answer 3

• An electron microscope can magnify an object up to 200000 times its original size.
• It produces black and white electron micrographs.

Question 4

What is a protoplasm?

Answer 4

• A protoplasm is a living material found in a cell and the protoplasm of a cell is made up of the cell membrane, cytoplasm and nucleus.

Question 5

What are the main parts of a plant and an animal cell?

Answer 5

ACRONYM: MVCCN (My Very Close Cousin Named)
- The main parts of a plant and an animal cell include the mitochondrion, vacuole, cytoplasm, cell membrane and the nucleus.

Question 6

What are the descriptions and functions of the cell wall?

Answer 6

The cell wall is:
- The outermost part of the cell.
- Made up of cellulose (sugar).
- Fully permeable to small molecules, so it does not allow ANY small molecules to pass through it.
The cell wall:
- Protects the cell from injury.
- Gives the cell its shape.

Question 7

What are the descriptions and functions of the cell membrane?

Answer 7

The cell membrane is:
- A partially permeable membrane that surrounds the cytoplasm.
- Is made up of lipids (fats) and proteins.
The cell membrane:
- Controls substances entering or leaving the cell.

Question 8

What are the descriptions and functions of the cytoplasm?

Answer 8

The cytoplasm is:
- A jelly-like substance embedded with organelles, which are specialised structures in the plant. (so, the cytoplasm contains organelles)
In the cytoplasm:
- Each organelle is specialised for a particular function
(e.g.) The cell wall helps to protect the cell from damage, and it gives the cell its shape because it is very rigid and hard.
- It is a site where most cellular activities occur and take place.
(e.g.) Cellular respiration, photosynthesis.

Question 9

What are the descriptions and functions of the nucleus?

Answer 9

The nucleus:
- Is surrounded by the nuclear membrane.
- Contains genetic material in the form of chromosomes.
The nucleus:
- Controls cell activities such as growth, and tissue repair.
- Is important for cell division.

Question 10

What is a nuclear membrane?

Answer 10

The nuclear membrane:
- Is a double-layered membrane that separates the nucleus from the cytoplasm in eukaryotic cells
- Is made out of two lipid bilayer membranes.
- Is selectively (not always) permeable, so it allows only certain molecules to pass through it.
- Contains nuclear pores that allow for the exchange of materials between the nucleus and the cytoplasm.
- Plays a crucial role in protecting the genetic material of the cell from the chemical reactions that occur outside the nucleus.
- Contains many proteins that are used in organizing DNA and regulating genes.

Question 11

What is an organelle?

Answer 11

• An organelle is a tiny structure embedded in the cytoplasm that carries different and specific functions.

Question 12

Does a plant cell have a cell wall?

Answer 12

• Yes

Question 13

Does an animal cell have a cell wall?

Answer 13

• No

Question 14

Does a plant cell have chloroplasts?

Answer 14

• Yes in leaves, but No in roots.
  Reason: There are chloroplasts in leaves so that they can take in sunlight during the day to photosynthesize and make food. However, there are no chloroplasts in the roots as they do not need to photosynthesize and make food for the plant, they only need to absorb water and mineral salts from the soil, anchor the plants to the soil, and to support the plant.

Question 15

Does an animal cell have chloroplasts?

Answer 15

• No

Question 16

Does a plant cell have vacuoles?

Answer 16

• Yes, it has one large central vacuole.

Question 17

Does an animal cell have vacuoles?

Answer 17

• Yes, it has small and many vacuoles.

Question 18

What are the descriptions and functions of the mitochondrion?

Answer 18

The mitochondrion is:
- A small oval or sausage-shaped structure.
- Enclosed by a double membrane.
- An inner membrane that is highly folded
The mitochondrion:
- Is a site where aerobic respiration occurs.
- Provides energy for cell activities like growth and reproduction.

Question 19

What is aerobic respiration?

Answer 19

• Aerobic respiration is a metabolic process that occurs in the presence of oxygen, where glucose and other food molecules are broken down into simpler molecules such as carbon dioxide and water.
• Afterwards, it releases energy that can be used by the body’s cells.

Question 20

What are the descriptions and functions of the endoplasmic reticulum (ER)?

Answer 20

1. Rough endoplasmic reticulum (RER):
   The Rough endoplasmic reticulum is:
   - A network of flattened spaces lined with a membrane.
   - Connected to the nuclear envelope.
   - Looks ‘rough’ as the ribosomes, small round structures are attached to its outer surface.
   The Rough endoplasmic reticulum:
   - Uses vesicles to transport proteins made by the ribosomes to the Golgi body.
   - (extra point, not the function of the Rough endoplasmic reticulum): Ribosomes found freely throughout the cytoplasm synthesize and make proteins for use within the cell.
2. Smooth endoplasmic reticulum (SER):
   The smooth endoplasmic reticulum:
   - Is a tube-like structure.
   - Is connected to the rough endoplasmic reticulum (RER)
   - Looks ‘smooth’ as no ribosomes are found on its surface.
   The smooth endoplasmic reticulum:
   - Synthesises fats and steroids (sex hormones in mammals).
   - Converts harmful substances to harmless substances through detoxification.

Question 21

What is detoxification?

Answer 21

• Detoxification is a process of removing toxic substances from the body.
• It can refer to the medical treatment of an alcoholic, or a drug addict involving abstention from drinks or drugs until the bloodstream is free of toxins.
• It is also the process of removing toxic substances from the environment

Question 22

What are the descriptions and functions of the Golgi body?

Answer 22

The Golgi body is:
- A stack of flattened spaces surrounded by membranes.
- Surrounded by numerous spherical body vesicles.
The Golgi body:
- Processes fats and proteins made in the rough and smooth endoplasmic reticulum.
- Stores and packages them in vesicles which transports them out of the cell.

Question 23

What are the descriptions and functions of a vacuole? (present in plants and animals)

Answer 23

The vacuole:
- Is a fluid-filled space.
- Is large and central in a plant cell, which is enclosed by a partially permeable membrane.
- Contains cell sap.
- (This point only applies to the vacuoles in animal cells) Is small and numerous in animal cells, which are enclosed by a membrane, and it exists temporarily.
The vacuole:
- In a plant contains cell sap, which contains dissolved sugars, mineral salts, and amino acids. (starch + minerals + proteins
- In animal cell, they store water and food substances.

Question 24

What are the descriptions and functions of chloroplasts?

Answer 24

Chloroplasts:
- Has an oval structure.
- Contains chlorophyll, a green pigment that is present in stacks of membranes.
Chloroplasts:
- Is the site of photosynthesis which is a process whereby plants make food and photosynthesize.
- Contains chlorophyll which is essential for photosynthesis.

Question 25

What is an organism?

Answer 25

• An organism is made up of different types of cells which have specific functions.

Question 26

What is a specialised cell?

Answer 26

• A specialized cell is a cell that has gone through differentiation.
• They develop special structures or lose certain (cell) structures to enable them to carry out specific functions.

Question 27

What is differentiation?

Answer 27

• It is a process in which a less specialized cell develops or matures to become more distinct in form and function.
• It involves the differential activation of some genes and the repression of others.
• Differentiation changes the function, size, shape and metabolic activity of the cell.

Question 28

What are the functions of a red blood cell?

Answer 28

A red blood cell:
- Transports oxygen to all parts of the body.
Adaptation:
A red blood cell:
- Contains haemoglobin, a red pigment that transports oxygen.
- Has a circular and biconcave shape. This increases the surface area-to-volume ratio of the cell which increases the rate of oxygen diffusion.
- Is flexible and can squeeze through small blood vessels.
- Does not have a nucleus which increases the amount of haemoglobin that is carried in the red blood cell.

(Extra point about the functions of haemoglobin):
(- It transfers oxygen from the lungs to tissue cells throughout the body and also carries carbon dioxide from the cells back to the lungs.)
(- It is an iron-containing protein in red blood cells that gives blood its red colour.)
(- It maintains the shape of red blood cells.)

Question 29

What is a root hair cell?

Answer 29

A root hair cell:
- Absorbs water and mineral salts from the soil.
A root hair cell:
- Has a long and narrow root hair extension which increases the surface area-to-volume ratio of the cell which increases the rate of absorption of water and mineral salts.

Question 30

What is a muscle cell?

Answer 30

A muscle cell:
- Causes muscle contractions to produce movement.
A muscle cell:
- Contains many mitochondria which provides energy for muscle contractions.

Question 31

What is a tissue?

Answer 31

• A tissue is a group of similar cells working together to perform an specific function.

Question 32

What is a SIMPLE tissue?

Answer 32

• A SIMPLE tissue consists of cells of the same type. (tissues that are made up of one type of cell)

(Example):
1. Parenchyma: are living cells with thin cell walls, oval or round in shape, found in soft parts of plants.
2. Collenchyma: are living cells with thickened corners of cell walls, elongated in shape, found in stems and leaves of plants.
3. Sclerenchyma: are dead cells with very thick cell walls due to lignin, found in hard parts of plants.
4. Simple squamous epithelium: are flat cells with thin membranes, found in the lining of blood vessels and body cavities.)

Question 33

What is a COMPLEX tissue?

Answer 33

• A COMPLEX tissue consists of more than one type of cell. (tissues that are made up of more than one type of cell)

(Example):
1. Xylem: It is made up of tracheas, xylem parenchyma, xylem fibers, and vessels. It transports water and minerals.
2. Phloem: It is made up of sieve tubes, companion cells, sieve cells, phloem fibers, and the phloem parenchyma. It carries food from the leaves to the rest of the plant.

Question 34

What is an organ?

Answer 34

• An organ is formed when different tissues combine.
  (An organ is formed from the combination of different tissues)

Question 35

What is an organ system?

Answer 35

• Organs work together in organ systems
• E.g. The digestive system. It involves organs such as the mouth, oesophagus, stomach, and intestines (small/large) working together to digest food.

Question 36

What is a multicellular organism?

Answer 36

• A multicellular organism is made up of many organ systems working together.
• E.g. The digestive, circulatory, respiratory, nervous, endocrine, muscular, skeletal, and reproductive systems work together to help a normal human body function well.