Cells are the smallest structural and functional unit of life. A single cell can carry out all the characteristics of a living thing.
An animal cell is different from a plant cell. Almost all cells contain nuclei. Exceptions include red blood cells as they do not have a nucleus in order to efficiently carry out their functions which will be discussed in an upcoming chapter.
A cell consists of protoplasm which includes cell membrane, cytoplasm and nucleus along with double membrane organelles. It's where all the biochemical reactions take place in the cell.
AN OVERVIEW OF ALL CELL STRUCTURES
The NUCLEUS is a a tiny spherical mass of denser protoplasm called nucleoplasm- consisting of a network of long thread-like structures known as chromatin that contain hereditary material such as DNA. Chromatins can condense to form highly coiled rod-shape structures called chromosomes. Along with it is the largest part of the nucleus-a smaller spherical structure called nucleolus (plural: nucleoli). All this is surrounded by the nuclear envelope.
FUNCTIONS OF NUCLEUS:
The nucleus is commonly referred to as the 'headquarter' of the cell's as it controls all cell activities such as repair and reproduction of the cell. As it contains genetic material, it is responsible for inheritance. All proteins are made by the chromosomes.
*NOTE- Ribosomes are also sites of protein synthesis.
The CYTOPLASM is a gel-like substance that usually occupies most of the cell.
FUNCTIONS OF CYTOPLASM:
Most of the chemical reactions occur here. As it is a suspension, it holds the cell structures together and prevents them from mixing up. 90% of the cytoplasm is water.
The CELL SURFACE MEMBRANE is a thin and flexible membrane that surrounds the inner structures i.e cytoplasm.
FUNCTIONS OF CELL MEMBRANE
The cell membrane is partially permeable. Meaning, it controls the entry and exit of substances of the cell- allowing only required substances to move in or out. It also holds and protects inner structures and provides identification to the cell.
Double-membrane organelles such as MITOCHONDRIA or CHLOROPLASTS may also be present.
FUNCTIONS OF MITOCHONDRIA (singular: mitochondrion)
It is commonly referred to as the powerhouse of the cell because it carries out aerobic respiration to produce large amounts of energy which may temporarily be stored in small adenosine triphosphate (ATP) molecules.
FUNCTIONS OF CHLOROPLASTS
They contain a green pigment called chlorophyll which traps the energy from sunlight for photosynthesis.
Sometimes for some organisms an external CELL WALL is also present. The substance from which it is made of can vary. E.g plant cell walls are made of cellulose (carbohydrate) while a fungus cell wall is made of chitin (protein).
FUNCTIONS OF CELL WALL
It is completely permeable and allows all substances to enter and exit through it. It provides strength and protection and is also responsible for the cell's turgidity.
A vacuole is a a fluid-filled space- usually containing cell sap or water and food.
FUNCTIONS OF VACUOLE
It maintains water potential.
Pairs of minute structures called CENTRIOLES can also be found near cell nuclei.
FUNCTIONS OF CENTRIOLES
They are involved in cell division.
The above were ALL different kinds of structures which may be present inside a living cell. As mentioned before, a plant cell is different from an animal cell. It means that their structures are different, but some structures are common for both.
SIMILARITIES BETWEEN ANIMAL AND PLANT CELLS
They all have:
- a nucleus
- cell membranes
- cytoplasm
- mitochondria
[ Image source: Google ]
Q. HOW IS AN ANIMAL CELL DIFFERENT FROM A PLANT CELL or HOW IS A PLANT CELL DIFFERENT FROM AN ANIMAL CELL?
Ans:
• Plant cells have a cellulose cell wall while animal cells don't.
• Plant cells have chloroplasts which animal cells don't.
• Plant cells have large central vacuoles while animal cells may or may not have vacuoles and if so, many small temporary ones.
• Plant cells have a fixed shape while animal cells have a variable shape.
• Plant cells have their nucleus at a side while animal cells have their nucleus in the centre.
• Plant cells usually don't contain centrioles while animal cells do.
[ Image source: Google ]
Specialization of certain cells help them adapt to perform their functions efficiently, such as root hair cells, xylems and red blood cells. Further detail of them will be covered in separate chapters namely TRANSPORT IN PLANTS and TRANSPORT IN MAMMALS.
CELL ORGANIZATION
A multicellular organism such as a human is made up of many cells.
cells->tissues->organs->organ systems->organism
A group of cells of same origin and structure working together to perform a particular function is known as a tissue. Example: nerve tissue, epithelial tissue, muscular tissue, epidermis (in plants) etc.
A group of different tissues working together to carry out a particular task is called an organ. Example: heart, liver, brain etc.
A group of different organs working together to carry out a particular function is known as an organ system. Example: nervous system, respiratory system, digestive system etc.
Lastly, a group of organ systems working together make up an entire organism.
End of Chapter
We all love easy chapters! Hope this book is helping you <3 Please don't forget to share our book with people.
{FEEL FREE TO ASK QUESTIONS! Subscribe to our YouTube channel where we curate the best videos on the hardest O-Level science and mathematics topics. Make sure to follow us on Instagram & Facebook
@ biobyaiesha for more!}