Cell: The Building Block of Life: questions with answers

Similar cells form tissues, tissues form organs, and several organs work together in an organ system. The cell remains the starting structural and functional unit.

Organisation combines the work of many cells but does not replace their functions. Cells provide both structure and function in living organisms.

Cell theory states that organisms are made of one or more cells, the cell is the basic structural and functional unit, and new cells arise from pre-existing cells.

Cell division is the process through which new cells form from cells that already exist. This is the third claim of classical cell theory.

Diffusion is the net movement of particles from higher to lower concentration and does not require a membrane. Osmosis specifically concerns water crossing a selectively permeable membrane.

Osmosis is the diffusion of water through a selectively permeable membrane. The net movement of water is from the dilute side, which has more water and less solute, towards the concentrated side, which has less water and more solute.

The cell membrane selectively controls entry into and exit from the cell. The cell wall provides support and permits water and many dissolved substances to pass. The other membranes enclose internal compartments.

Every living cell is enclosed by a cell membrane, so it is common to both cells. The cellulose cell wall and the large central vacuole are plant features, and the nucleoid belongs to a bacterial cell.

DNA carries genetic information, and genes are its functional segments. DNA associated with proteins appears as chromatin in a non-dividing cell and becomes organised into visible chromosomes before division.

The DNA was already present as chromatin in the non-dividing cell. Before division, that material becomes organised into visible chromosomes.

A nucleoid contains the prokaryotic cell's DNA without a nuclear membrane. The absence of a true nucleus and membrane-bound organelles identifies the cell as prokaryotic.

A bacterial cell does have genetic material. Its DNA lies in a region of the cytoplasm called the nucleoid. No nuclear membrane surrounds this region, so the nucleus is not a true one.

Only chloroplasts contain chlorophyll and use light to make food. Leucoplasts are colourless plastids that store food, and mitochondria release energy from food.

Mitochondria break down food to release energy the cell can use. Chloroplasts, not mitochondria, use sunlight to make food, and energy cannot be made from nothing.

Mitosis produces two genetically identical daughter cells with the same chromosome number as the parent cell. Meiosis is a two-step division that produces four gametes with half that number. Two rounds of mitosis would give four cells, and the first step of meiosis alone would give two cells with half the chromosome number.