Grade 8 Science Exploring Cells and Their Functions

What is the basic unit of life according to cell theory?

• Tissue

• Cell

• Organ

• Organism

Answer explanation

According to cell theory, the cell is the basic unit of life. It is the smallest structural and functional unit of an organism, making 'Cell' the correct answer.

Which scientist is credited with coining the term "cell"?

• Louis Pasteur

• Robert Hooke

• Anton van Leeuwenhoek

• Rudolf Virchow

Answer explanation

Robert Hooke is credited with coining the term "cell" in 1665 after observing cork under a microscope. He described the small, box-like structures he saw, which reminded him of the cells inhabited by monks.

Which of the following is NOT a part of the cell theory?

• All living things are composed of cells.

• Cells are the basic unit of structure and function in living things.

• All cells arise from pre-existing cells.

• Cells can spontaneously generate from non-living material.

Answer explanation

The statement 'Cells can spontaneously generate from non-living material' is NOT part of cell theory. Cell theory states that all living things are made of cells, and all cells arise from pre-existing cells.

Who proposed that all cells come from pre-existing cells?

• Matthias Schleiden

• Theodor Schwann

• Rudolf Virchow

• Louis Pasteur

Answer explanation

Rudolf Virchow proposed that all cells arise from pre-existing cells, emphasizing the continuity of life. This principle is a key component of the cell theory, which he helped to establish.

Which of the following structures is found in plant cells but not in animal cells?

• Nucleus

• Cell wall

• Mitochondria

• Ribosome

Answer explanation

The cell wall is a rigid structure found in plant cells that provides support and protection. In contrast, animal cells lack a cell wall and only have a flexible cell membrane.

What is the function of the mitochondria in a cell?

• Protein synthesis

• Energy production

• Photosynthesis

• Cell division

Answer explanation

The mitochondria are known as the powerhouse of the cell, as their primary function is energy production through the process of cellular respiration, converting nutrients into ATP, the energy currency of the cell.

Which organelle is responsible for photosynthesis in plant cells?

• Chloroplast

• Mitochondria

• Nucleus

• Golgi apparatus

Answer explanation

The chloroplast is the organelle in plant cells responsible for photosynthesis, converting sunlight into energy. Mitochondria generate energy, the nucleus contains genetic material, and the Golgi apparatus modifies proteins.

What is the semi-permeable membrane that surrounds the cell called?

• Cell wall

• Cytoplasm

• Cell membrane

• Nucleus

Answer explanation

The semi-permeable membrane that surrounds the cell is called the cell membrane. It regulates the movement of substances in and out of the cell, unlike the cell wall, which is rigid and found in plant cells.

Which of the following is a function of the cell membrane?

• Provides energy to the cell

• Controls the movement of substances in and out of the cell

• Synthesizes proteins

• Stores genetic information

Answer explanation

The cell membrane primarily functions to control the movement of substances in and out of the cell, maintaining homeostasis. The other options relate to energy production, protein synthesis, and genetic storage, which are not membrane functions.

What is the jelly-like substance inside the cell that holds organelles in place?

• Nucleus

• Cytoplasm

• Cell wall

• Chloroplast

Answer explanation

The jelly-like substance inside the cell that holds organelles in place is called cytoplasm. It provides a medium for biochemical reactions and supports the cell's structure, unlike the nucleus, cell wall, or chloroplast.