How do plants and animals continue to grow all their lives? Do all cells in a plant divide all the time? Do you think all cells continue to divide in all plants and animals? Can you tell the name and the location of tissues having cells that divide all their life in higher plants? Do animals have similar meristematic tissues?
(i) Plants and animals grow throughout their lives through mitosis. In plants, mitotic divisions in meristematic tissues (apical and lateral cambium) result in continuous growth throughout their life.
(ii) No, all cells in a plant do not divide all the time. Only meristematic tissues have cells that divide continuously.
(iii) No, all cells do not continue to divide in all plants and animals. In animals, cells like heart cells do not exhibit division, while many others divide only occasionally to replace cells lost due to injury or cell death. These non-dividing cells exit G₁ phase to enter an inactive stage called quiescent stage (G₀).
(iv) The tissues having cells that divide all their life in higher plants are called meristematic tissues, located at the apical and lateral cambium.
(v) No, animals do not have similar meristematic tissues. Instead, specific cells like those of the upper layer of epidermis, lining of the gut, and blood cells are constantly replaced through mitosis for cell repair.
Explanation
The textbook explains that growth in multicellular organisms is due to mitosis. Plants have specialized meristematic tissues (apical and lateral cambium) that continuously divide, enabling lifelong growth. However, not all plant cells divide continuously. In animals, the situation differs - some cells like heart cells do not divide at all, while others divide only occasionally for repair. Non-dividing cells enter the G₀ (quiescent) stage. Animals lack meristematic tissues but maintain certain cell populations (epidermis, gut lining, blood) that are constantly replaced through mitosis.