Olympiad Test: Cell - Structure And Functions - 1 - Class 8 MCQ

Answer:
The structural and functional unit of all living beings is the cell. Here is a detailed explanation:
1. Definition of a cell:
- A cell is the smallest structural and functional unit of an organism.
- It is the basic building block of life.
2. Characteristics of cells:
- Cells are microscopic in size and cannot be seen with the naked eye.
- They have a specific shape and structure that allows them to perform various functions.
- Cells have a plasma membrane that separates the internal contents from the external environment.
- They contain genetic material, such as DNA, which carries the hereditary information.
3. Types of cells:
- There are two main types of cells: prokaryotic cells and eukaryotic cells.
- Prokaryotic cells, such as bacteria, do not have a nucleus or membrane-bound organelles.
- Eukaryotic cells, found in plants, animals, fungi, and protists, have a true nucleus and various organelles.
4. Functions of cells:
- Cells carry out various functions necessary for the survival of living organisms.
- They can reproduce, grow, and differentiate into specialized cell types.
- Cells obtain nutrients, eliminate waste, and exchange gases with the external environment.
- They can respond to stimuli and maintain homeostasis.
- Cells also play a role in the overall functioning of tissues, organs, and organ systems.
In conclusion, the cell is the structural and functional unit of all living beings. It is the smallest unit of life that carries out various functions necessary for the survival of organisms.

Explanation:
Introduction:
The question asks for the classification of the hen's egg in terms of its biological structure. It provides four options: tissue, cell, organ, and organ system.
Answer:
The correct answer is cell.
Explanation:
To understand why the egg of a hen is classified as a cell, we need to consider its structure and function.
Egg Structure:
1. The outermost layer of the egg is the shell, which provides protection.
2. Underneath the shell is the shell membrane, which acts as a barrier against bacteria.
3. The egg white, or albumen, surrounds the yolk and provides nutrients for the developing embryo.
4. The yolk contains the necessary nutrients for the developing embryo.
5. The germinal disc or blastodisc is a small, circular area on the surface of the yolk where fertilization occurs.
Egg Function:
1. The primary function of the hen's egg is reproduction.
2. It contains all the necessary genetic material and nutrients for the development of a new organism.
Why is it a cell?
1. A cell is the basic structural and functional unit of all living organisms.
2. The egg of a hen meets this criterion as it is a single structure that performs all the necessary functions of life.
3. The egg has a membrane that separates its internal contents from the external environment, just like a typical cell.
4. The yolk contains all the necessary organelles and genetic material for the development of a new organism.
5. Fertilization occurs within the egg, resulting in the fusion of genetic material and the initiation of embryonic development.
In conclusion, the egg of a hen is classified as a cell because it meets the criteria of being a basic structural and functional unit of life. It contains all the necessary components for reproduction and embryonic development.

Answer:
To determine which of the given options is multicellular, we need to analyze each option individually.
A: Amoeba
- Amoeba is a unicellular organism, meaning it is composed of a single cell.
B: Paramecium
- Paramecium is also a unicellular organism.
C: Bacteria
- Bacteria, like Amoeba and Paramecium, is a unicellular organism.
D: Mushroom
- Mushrooms are multicellular organisms.
- They are made up of a network of thread-like structures called hyphae, which collectively form the mycelium.
- The mycelium is the vegetative part of the fungus and can give rise to the reproductive structures, which are the mushrooms themselves.
Based on the analysis, option D (Mushroom) is multicellular, while options A (Amoeba), B (Paramecium), and C (Bacteria) are all unicellular.

Not Present in Animal Cells:
- Plastid: Plastids are organelles found in plant cells that are involved in various functions such as photosynthesis, storage of pigments, and synthesis of lipids. They are not present in animal cells.
- Large Vacuoles: Vacuoles are membrane-bound sacs found in cells that play a role in storage, waste disposal, and maintaining cell turgidity. While animal cells do contain vacuoles, they are generally smaller and more numerous compared to the large central vacuole found in plant cells.
- Cell Wall: The cell wall is a rigid structure found in plant cells that provides support and protection. Animal cells do not have a cell wall; instead, they have a flexible cell membrane that surrounds and protects the cell.
Therefore, the correct answer is D: All of these as all the options (plastid, large vacuoles, and cell wall) are not present in animal cells.

Instrument used to see onion peel cells on a slide:

Microscope

Explanation:
To see onion peel cells on a slide, a microscope is used. A microscope is an instrument that magnifies small objects, allowing us to observe them in detail. Here is a detailed explanation:
- Microscope: A microscope is a scientific instrument that is used to magnify small objects, making them visible to the human eye. It consists of an eyepiece, objective lenses, and a light source.
- Onion Peel Cells: Onion peel cells are commonly used in biology labs for microscopic observation. They have a transparent structure that allows us to easily visualize their cellular components.
- Preparation: To view onion peel cells, a thin layer of onion peel is placed on a glass slide. A drop of water or a staining solution may be added to enhance visibility. A coverslip is then placed on top to protect the sample.
- Microscopic Observation: The prepared slide is then placed on the stage of the microscope. The objective lens is selected based on the desired magnification. By adjusting the focus and using the coarse and fine adjustment knobs, the cells on the slide can be brought into clear focus.
- Cellular Structures: Under the microscope, onion peel cells can be observed to have a rectangular shape with distinct cell walls. The cytoplasm and nucleus can also be seen, along with any other cellular structures of interest.
In conclusion, a microscope is the instrument used to see onion peel cells on a slide. It allows us to observe the cellular structures and details of the onion peel cells, aiding in the study of plant biology.

Cell organelle that contains chlorophyll and is present in plant cells is:
The correct answer is Chloroplast.
Explanation:
Chloroplasts are specialized organelles found in plant cells that are responsible for photosynthesis, the process by which plants convert sunlight into energy. Here's a more detailed explanation:
- Chloroplast structure: Chloroplasts are double-membraned organelles, meaning they have an outer and inner membrane. Inside the chloroplast, there are stacks of disc-like structures called thylakoids, which contain chlorophyll and other pigments.
- Function: Chloroplasts are the sites of photosynthesis in plant cells. They capture light energy from the sun and convert it into chemical energy in the form of glucose. This process involves the absorption of sunlight by chlorophyll, which is then used to power the synthesis of glucose from carbon dioxide and water.
- Chlorophyll: Chlorophyll is a green pigment found in chloroplasts that plays a key role in photosynthesis. It absorbs light energy from the sun and uses it to convert carbon dioxide and water into glucose and oxygen.
- Photosynthesis: Photosynthesis is a complex process that occurs in the chloroplasts. It involves two main stages: the light-dependent reactions and the light-independent reactions (also known as the Calvin cycle). The light-dependent reactions occur in the thylakoid membranes and involve the absorption of light energy, which is used to generate ATP and NADPH. These energy-rich molecules are then used in the light-independent reactions to convert carbon dioxide into glucose.
In conclusion, the cell organelle that contains chlorophyll and is present in plant cells is the chloroplast.

Answer: C: Chloroplast
Explanation:
An animal cell is a eukaryotic cell that lacks a cell wall and chloroplasts, which are found in plant cells. Here is a detailed explanation of each option:
1. Mitochondria: Mitochondria are present in animal cells. They are membrane-bound organelles responsible for producing energy in the form of ATP through cellular respiration.
2. Cell membrane: The cell membrane, also known as the plasma membrane, is present in animal cells. It surrounds the cell, providing structural support, regulating the passage of materials in and out of the cell, and maintaining homeostasis.
3. Chloroplast: Chloroplasts are not present in animal cells. They are organelles found in plant cells responsible for photosynthesis, the process by which plants convert sunlight into energy.
4. Nucleus: The nucleus is present in animal cells. It is a membrane-bound organelle that contains the cell's genetic material, including DNA. The nucleus controls the cell's activities and is involved in cell division.
In summary, chloroplasts are not present in animal cells, while mitochondria, cell membrane, and nucleus are all present.

Cell Components:
- Cytoplasm: It is the jelly-like substance that fills the cell and contains various organelles.
- Nucleus: The nucleus is the control center of the cell and contains genetic material (DNA) that regulates cell activities.
- Chromosome: Chromosomes are structures made of DNA that carry genetic information. They are located in the nucleus.
- All of these: The correct answer is option D, as all the mentioned components (cytoplasm, nucleus, and chromosome) are present in a cell.
In summary, a cell contains cytoplasm, nucleus, and chromosomes, which collectively contribute to the functioning and genetic regulation of the cell.

The control center of a cell is called the nucleus.
The nucleus plays a crucial role in controlling the activities of the cell. It contains the cell's genetic material, which is organized into structures called chromosomes. These chromosomes carry the instructions for the cell's functions and determine its characteristics.
Key Points:
- The nucleus is often referred to as the control center of the cell.
- It contains the cell's genetic material, including DNA and RNA.
- The nucleus controls the cell's activities by regulating gene expression.
- It is surrounded by a nuclear membrane, which separates it from the cytoplasm.
- The nucleus also contains a nucleolus, which is responsible for producing ribosomes.
- The nucleus is involved in processes such as cell division and protein synthesis.
Therefore, the correct answer is A: nucleus.

Introduction:
A cell is the basic structural and functional unit of all living organisms. Cells can be classified into two main types based on their structure and organization of genetic material: eukaryotic cells and prokaryotic cells. Let's explore the characteristics of each type.
Eukaryotic Cell:
- Eukaryotic cells are found in plants, animals, fungi, and protists.
- They have a distinct nucleus that houses the genetic material (DNA) and is enclosed by a nuclear membrane.
- The DNA in eukaryotic cells is organized into multiple linear chromosomes.
- Eukaryotic cells are generally larger and more complex in structure compared to prokaryotic cells.
- They contain various membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.
- Eukaryotic cells undergo complex processes such as mitosis and meiosis for cell division.
Prokaryotic Cell:
- Prokaryotic cells are found in bacteria and archaea.
- They do not have a true nucleus. Instead, the genetic material is present as a circular DNA molecule in the cytoplasm.
- Prokaryotic cells lack membrane-bound organelles. However, they may have specialized structures such as ribosomes, cell walls, and flagella.
- Prokaryotic cells are typically smaller and simpler in structure compared to eukaryotic cells.
- They reproduce through binary fission, a simple form of cell division.
Both (a) and (b):
- Some cells can exhibit characteristics of both eukaryotic and prokaryotic cells. For example:
- Mitochondria, which are organelles found in eukaryotic cells, have their own circular DNA and replicate independently, similar to prokaryotic cells.
- Certain algae, such as cyanobacteria, have prokaryotic characteristics but also possess specialized structures like chloroplasts, which are found in eukaryotic plant cells.
Conclusion:
In summary, cells can be classified into two main types: eukaryotic cells and prokaryotic cells. Eukaryotic cells are complex, contain a nucleus, and have various organelles, while prokaryotic cells are simpler and lack a true nucleus. However, some cells may exhibit characteristics of both types, blurring the line between eukaryotes and prokaryotes.