There are few millions to billions of cells in an animal body based on its weight and size.
Animal cells are unique than the plant cells in many aspects.
Unlike in plants, there are different types of cells with diverse functions.
They vary based on the body organ and type of tissue they form.
Animal Cell Facts
1. Lack of nucleus: Animal cells are eukaryotic and have a prominent nucleus. But, not all cells have the nucleus in them. For example, red blood cells have no nucleus. Hence, they are called red blood corpuscles instead of cells. They are formed from the bone marrow tissue. These RBC cells do not need a nucleus as they are not going to multiply by mitosis or meiosis. Also, the hemoglobin inside them occupies most of the space. Besides, RBC also lack mitochondria and other cell organelles. Similarly, in vascular plants, the sieve tube cells lack a nucleus.
2. Totipotency: This is the ability of the cells to convert into any other required cell in the body. Stem cells are the ones which are totipotent. They can be found in dental growth tissue, placenta, umbilical cord blood of newborn babies. In the body, these stem cells convert into cells as per the organ needs. Thus, they help to repair damaged tissue or replace a worn out tissue.
3. Ability to swim: Some animal cells can swim when required. Protozoans are examples of the cell which can swim. Besides, sperm cells which have the male gamete are also able to swim. Once released, they swim towards the ova in the uterus and merges with it.
They have a tail which enables them to swim effectively.
4. Receptors: Most cells have plasma membranes which have receptors. Receptors, as the name indicates, are structures which can receive a signal from external stimuli. These are protein structures which receive a signal from external agents and convey it into the cell. This is how the drugs act at the cellular level and bring the required effects. There are four types of receptors in animal bodies with diverse functions.
5. Telomer decides lifespan: Telomeres are the repetitive nucleotide sequences present at the end of each chromosome. These protect the ends of the chromosome from damage and abnormal fusion with other chromosomes.
As you know, the cell divides by the processes of mitosis and multiplies in numbers. For each cell division, the telomere length goes down and it decides the lifespan of a cell. As per Hayflick limit, a cell can undergo approximately 40 to 60 divisions by mitosis. Then after, it goes for the senescence phase and dies by programmed cell death. Cell life also depends on stress, health, nutrition, and other conditions.
6. Self-repair: During the process of physiology and daily life activities, the cell tends to have some malfunctions. This happens in terms of abnormalities in DNA strand, RNA strand, protein arrangement, etc. But, of them, DNA repair is crucial and happens almost every day. The cells immediately correct the malfunction for their stability. If unable to correct, they go for self-destruction.
7. Self-destruction: As mentioned before, cells can trigger death on to themselves. When there is an injury to the cells or a faulty DNA is formed, they go for self-destruction to avoid damage to other cells. This self-destruction occurs by a process called apoptosis.
8. Lack of cell division: Animals cells undergo either mitosis or meiosis to multiply their numbers. But nerve cells are an exception. They never divide or multiply once formed during birth. If there is damage; they try to innervate the surrounding area by the process called nerve plasticity.
9. Chemotaxis activity: This a mechanism by which cells move towards one part of the body due to chemical signals. This is seen in the case of white blood cells. When there is an infection or wound in one part of the body, the WBC cells migrate to that point for defense and repair. Hence you will notice pus in the area of wounds, infections or even cancer. The intention of migration is to kill the pathogens, produce histamine and enhance the repair process. Hence, you will notice the sense of itch at the point of the wound during healing.
10. Cell eating: Cells can eat by themselves. Macrophages and neutrophils are the type of white blood cells which engulf any harmful bacteria or toxins in the body. This cell eating is called phagocytosis. Neutrophils eat any harmful bacteria present in the blood circulation. While the macrophages engulf any pathogenic microbes in the tissues. Once eaten by these cells, the microbes are digested by the enzymatic action of lysosomes.
11. Cell drinking: Cell can also drink liquid material or substances by a process known as pinocytosis. This seen mostly in protozoa like the amoeba.
12. Cell content: Almost 70% of cell matter is made of water; the remaining portion is made of proteins, carbohydrates, lipids, micro-elements, etc.
13. Vision: Rod cells and cone cells are present in the eye to help in vision. They have a protein called, photoreceptor protein which absorbs the photons of light and induce changes in the membrane potential. Rod cells are very sensitive that they can be triggered by a single photon. The cats have six to eight times more rods than humans. Due to this, they can see in the dark at night.
On the other hand, insects have compound eyes and they have multiple visions. So, a single object appears as numerous objects to them.
14. Organelle location: The location or organelles varies based on the requirement of other factors. In nerve cells, the mitochondria are concentrated at the nerve endings to generate the energy required for signal transduction.