Question

The cytoplasm and nucleus are enclosed within the?

Answer 1

Hint: Cell is the structural and functional unit of life. The cell may be either prokaryotic or eukaryotic. A prokaryotic cell has no membrane bounded organelles and the nucleus is present in the form of circular ds DNA, ‘Nucleoid’ whereas, a eukaryotic cell has membrane bound organelles and the nucleus is also has double walled nuclear membrane. In all kinds of cells, a cell membrane is present that encloses all the cell materials. The cell is also lined by a cell wall in bacteria, fungi and plant cells. A cell without a cell wall is called a ‘protoplast’.

Complete answer:
A brief of cellular components are given below:
A typical eukaryotic cell has: membrane(s) enclosing them, double walled organelles, endo-membrane system, non-membrane bound organelles, nucleus, and cytoplasm.
Membranes:
1. Cell wall: It is a typical characteristic feature of plant cells. It mainly functions as the protective layer and has primary, secondary and may also have tertiary walls. The wall is made of different materials in different organisms. In plants, it is made of cellulose; in bacteria, of peptidoglycan; in fungi, of glucans, mannans, and glycoproteins.
2. Cell membrane: Also called ‘plasma membrane’. With time there have been many models of plasma membrane, the most famous and accepted of which is the “Fluid Mosaic Model” by Singer and Nicolson. The structure of cell membrane is almost similar in all organisms. The transport of molecules through the plasma membrane is the plasma membrane's most critical function.
3. Cytoplasm: It is the main arena of cellular activities. It has different organelles present in it. The process of glycolysis occurs here.
Endo-membrane system: It includes the single membrane organelles and is called so because the functions of these organelles are coordinated. It includes:
4. Endoplasmic Reticulum: It divides the cytoplasm into two compartments- luminal (inside ER) and extra- luminal (outside ER). It is involved in the GERL complex that is formation of lysosomes via Golgi bodies. It is of two types, ones that have ribosomes attached to their outer membrane and others don’t have ribosomes. The former is called Rough ER and is involved in protein synthesis and secretion & the latter are Smooth ER which are involved in lipid synthesis.
5. Golgi Bodies: These are densely stained reticular structures near the nucleus. It consists of many flat, disc-shaped sacs or cisternae. It has a cis or convex or forming face towards the nucleus and a trans or concave and maturation face towards cytoplasm. It is mainly involved in the packaging of materials, and glycolipid and glycoprotein synthesis.
6. Lysosomes: These are formed after the processing and packaging by Golgi bodies. They are mainly found in animal cells and have hydrolytic enzymes which are involved in digestion.
7. Vacuoles: Mainly found in plants and occupy central position and \[90\% \] of volume of the cell. The membrane of the vacuole is called a ‘tonoplast’. It contains water, sap, excretory products, and other non-cellular elements. It helps in maintaining the concentration gradient in plant cells.
8. Double Membrane organelle: These organelles are surrounded by double membrane- outer and inner. They are not part of the endo-membrane system because their functions are not coordinated with the other organelles.
a) Mitochondrion: It is the powerhouse of the cell. The process of respiration that provides us energy occurs in the matrix of mitochondria. It has outer and inner mitochondrial membrane, and peri-mitochondrial space exists between them.
b) Chloroplast: The chloroplasts contain chlorophyll and carotenoid pigments which are responsible for trapping light energy essential for photosynthesis. Plastids are found in plants only. Chloroplast is a kind of plastid that has flattened membranous sacs called the thylakoids, which are present in the stroma. Enzymes necessary for glucose and protein synthesis are found in the stroma of chloroplasts.
Both of these organelles have ribosomes, circular dsDNA and RNA fragments and are capable of dividing by binary fission.
c) Nucleus: Nucleus has the main genetic material of the cell. Nuclear envelope is also a double walled structure. The walls of the nucleus are disrupted in between by nuclear pores. Ribosomes are attached to the outer nuclear membrane. The cavity in the nucleus is nucleoplasm. The nucleoplasm has a membrane-less structure called ‘Nucleolus’ present in it. Nucleolus is the main site for rRNA synthesis. In the interphase stage the nuclear material is in extended/decondensed form- Chromatin. This during cell division condenses to form chromosomes. A cell may have one (uninucleate) or many (multinucleate) nuclei.
Ribosomes: These are membrane-less granular structures composed of rRNA and proteins. The ribosomes (‘Palade particles’) have different sediment coefficients in prokaryotes and eukaryotes. In prokaryotes the unit is \[70\]S (sub units- \[50\]S and \[30\]S) and in eukaryotes \[80\]S (sub units- \[60\]S and \[40\]S). \[70\]S ribosomes are also found in chloroplast and mitochondria of eukaryotic cells. They are the main site of protein synthesis.

The cytoplasm and nucleus are enclosed by the cell or plasma membrane. The cell membrane is further surrounded by a cell wall in plant cells.

Note:
A cell also has centrioles, centrosomes, other microbodies, inclusion bodies and some cells might also have cilia or flagella present in them. The cytoskeleton is an intricate network of filamentous proteinaceous structures found in the cytoplasm that includes microtubules, microfilaments, and intermediate filaments. During cell division in animal cells, the centrioles create the basal body of cilia or flagella, as well as spindle fibres that give rise to the spindle apparatus. Cellular mobility is aided by cilia and flagella.