Chapter 1 : Cells, Reproduction and Heredity
Cells are the basic structural units of all living organisms.
It is smallest unit of life, often called as the building block of life.
All living things are composed of cells.
Cell biology is also called life fundamental science.
Most cells are very small, so small that they can only be seen with the microscope.
Our body is composed of billions of cells! Within our body, cells have different functions.
We have a variety of cells in our body for example blood cells, skin cells, platelets, etc.
Cells found in animals and plants (with just a few exceptions) have these features in common:
Topics covered in this snack-sized chapter:
- Cell membrane which serves as a boundary between the cell and the outside environment
- The Cytoplasm is a gel-like substance within the cell membrane holding all the internal sub-structures of cell.
- Nucleus is a central structure of a cell that contains DNA inside them.
- Mitochondrion (plural, mitochondria), where cellular respiration takes place.
Plant cells have some additional features other than the ones listed above:
- Cellular respiration: The breakdown of sugar to produce energy for the cell, a process that uses oxygen and produces carbon dioxide and water.
- Chloroplast uses light energy to convert carbon dioxide molecules into one organic carbon sugar.
- Cell wall is outside the cell membrane which provides additional strength.
The life of eukaryotic cells is characterized by a cell cycle with two major phases:
During the interphase, the cell takes in nutrients, grows, and duplicates its chromosomes.
During the cell division phase, the nucleus divides in a process called mitosis and then the divided nuclei are established in separate cells in a process called cytokinesis.
Eukaryotic Cell Reproduction
Prokaryotic cells reproduce by a process called as binary fission.
The DNA in such cells is contained in a single circular chromosome called a plasmid within the cytoplasm.
The reproductive process starts with the replication of the chromosome.
The new chromosome attaches itself to the plasma membrane and the two chromosomes migrate to opposite ends of the cell.
The plasma membrane in the middle of the cell grows inward until it closes to separate the cell into two compartments, each with a full complement of genetic material.
The cell then "fissions" at the center, forming two new daughter cells
Cells are divided and new cell is formed, cells also have life cycle.
Cells reproduce themselves by dividing a “mother” cell into two “daughter” cells that are exactly like the mother cell.
Prokaryotic Cell Reproduction
- In this process before cell divides the mother cell makes two copies of each chromosome.
- This means that for a short time the mother cell has four complete pairs of 23 chromosomes.
- Cells having two pairs of chromosomes are called “diploids”
- Mother cell does this because when it divides, each daughter cell receives two pairs of chromosome.
- This cell division is called “mitosis”.
- Through mitosis, cells keeps on dividing-from one cell all the way to a trillions of cells.
- Some cells have only ONE pair of chromosome, these cells are called “haploid”.
- Haploid cells are made through a different type of cell division called “meiosis”.
- Meiosis begins with one diploid mother cell which divides into two daughter cells like mitosis.
Inside every cell of each living thing (plants or animals) is a set of instructions called genes.
The genes provide the instructions on what is the plant or animal, what it looks like, how it should survive, and how it will interact with its surrounding environment.
Most living things have pairs of chromosomes (one from each parent).
They may have different numbers of chromosomes from another living thing.
For example, humans have 23 pairs of chromosomes and the fruit fly has 4 pairs.
Genetics deals with molecular structure of genes.
- But in the next process daughter cell divides itself into four haploid cells without copying chromosome pairs. We need haploid cells for reproduction.
All humans look alike yet they are different from one another.
Heredity is the process by which an offspring cell or organism acquires or becomes activated to the characteristics of its parent cell or organism.