Basic science for class 8
Biology
Chapter - 2
The cell
Only answer.
### Short Answers (20 words or less)
1. **Unicellular organisms** are living entities made up of a single cell, like bacteria and protozoa.
2. **Staining specimens** increases contrast, making cells and their structures more visible under a microscope.
3. The four types of animal tissue are **epithelial, connective, muscle, and nervous**.
4. A **vacuole** is a membrane-bound organelle that stores nutrients, waste products, and maintains cell pressure.
5. **Chloroplasts** are found in **plant cells** and some algae for photosynthesis.
### Detailed Answers (40 words or less)
1. The cell is the **structural and functional unit of life** because it is the smallest unit that performs all life processes.
2. Plastids include **chloroplasts** (photosynthesis), **chromoplasts** (pigment storage), and **leucoplasts** (storage of starch, oils, proteins).
3. **Vascular bundles** consist of **xylem** (transports water, minerals) and **phloem** (transports nutrients, organic compounds).
4. The nucleus is called the control room of the cell because it contains DNA and regulates gene expression and cell functions.
5. The plasma membrane is called selectively permeable because it controls the entry and exit of substances, maintaining homeostasis.
### Short Answers (100 words or less)
1. **Basic Differences Between Plant and Animal Cells**:
Plant cells have a cell wall, chloroplasts, and a large central vacuole, while animal cells do not. Plant cells are usually rectangular, whereas animal cells are round. Plant cells can perform photosynthesis, while animal cells cannot. Animal cells have centrioles and lysosomes more commonly than plant cells.
2. **Regions in a Transverse Section of a Dicotyledonous Stem**:
Under the microscope, a transverse section of a dicotyledonous stem shows the epidermis (outer layer), cortex (layer beneath epidermis), vascular bundles (arranged in a ring), and the pith (central part). Vascular bundles contain xylem and phloem tissues.
### Multiple Choice
1. Cheek cells are:
- **(a) epithelial cells**
2. Vascular bundles are found:
- **(c) in roots, stems and leaves**
3. The cell wall in plant cells is made up of:
- **(d) cellulose**
4. Blood is a type of:
- **(b) connective tissue**
5. The brain and spinal cord are made up of:
- **(a) nervous tissue**
6. Red blood cells:
- **(d) do not have a nucleus**
### Fill in the Blanks
1. The dense tangle of chromosomes inside the nucleus is called **chromatin**.
2. Chromosomes carry **genes** which pass on hereditary characters.
3. The thin-walled oval cells extending from the epidermis to the vascular bundles form the **cortex**.
4. The matrix in which blood cells are suspended is called **plasma**.
5. A microscope has two lenses, called the objective and the **ocular (or eyepiece)**.
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