The walls of xylem cells are lignified (strengthened with a substance called lignin ). This allows the xylem to withstand pressure changes as water moves through the plant.
The cell membrane is flexible because of the presence of oil like substances called phospholipids, which gives it a fluid nature. While as the cell walls are rigid because of the presence of the thick layers of the substances like cellulose in plants, chitin in fungi and peptidoglycon in bacteria.
Answer:
The correct answer is - option B. They are small because they lack a nucleus.
Explanation:
Red blood cells or erythrocytes are specialized cell that produce in bone marrow and have specific role such as carrying oxygen from lungs to deliver it to the various organs and carry out carbon dioxide.
In mammals these cells lack cell organelles such as nucleus and mitochondria, a major factor that determined its smaller size. The size of RBC are move through narrow vessels throughout a organism because of its specific size and shape that provide it space for hemoglobin and allow to be flexible and bend to move through narrow vessels.
Thus, the correct answer is : option B. They are small because they lack a nucleus.
Land and water are the two natural resources will be most affected as people try to meet the growing demand for food.
Meeting the growing demand for food will involve planting more food crops and this will requires more lands. The planted crops will also need water in order to grow very well. Thus, more land and water will be needed to produce more food.
Answer:
Tropical areas are warm and wet causing for animals to want to hide essentially. Also there is a lot of cover for animals to hide in. Usually in tropical areas there are a lot of predators also, another reason for animals to hide.
