2.3 The Cell Interior โ€” A Coordinated Working System

Last updated at July 10, 2026 by

๐Ÿ’ฌ Think about it

Think of a busy kitchen. One person cooks, one washes, one packs. Each has a job, and together they run the kitchen. A cell is like that โ€” a tiny factory where every part does one special job. Let us look inside.

What are the three basic parts of most cells?
Three Basic Parts of a Cell Cell Plasma Membrane Selectively permeable outer boundary. Cytoplasm Semi-fluid, jelly-like substance inside. Nucleus Prominent control centre of the cell.
Cytoplasm Cyto Greek: cell Plasma Greek: fluid substance The jelly-like fluid that fills the cell and holds all the organelles.
  • A selectively permeable membrane (plasma membrane).
  • A semi-fluid, jelly-like cytoplasm.
  • A prominent nucleus.
Basic part What it is
Plasma membrane The selectively permeable outer boundary.
Cytoplasm A semi-fluid, jelly-like substance inside.
Nucleus A prominent control centre of the cell.
What are organelles?
Organelles Tiny sub-cellular parts held in the cytoplasm, each doing a specific job. Most are visible only under an electron microscope. e.g. A cell is like a tiny factory, with each part doing a specific job.
Organelle Organ tool / instrument (Greek: organon) elle small (French diminutive) A small specialised structure inside the cell โ€” each organelle is a tiny organ with its own specific job.
Image: A eukaryotic cell with its cytoplasm holding many tiny labelled organelles such as the nucleus, mitochondria, ribosomes and Golgi apparatus, each shown as a small worker doing a specific job.
  • The cytoplasm holds tiny sub-cellular parts called organelles.
  • Each organelle does a specific job.
  • Most are visible only under an electron microscope.
Example: A cell is like a tiny factory, with each part doing a specific job.
๐Ÿ”ง Activity 2.4 โ€” Let us study

In this Activity, we will study diagrams of a bacterial cell, a plant cell and an animal cell, and record which structures each one has.

Activity 2.4 โ€” Steps Step 1 Study diagrams of a bacterial, plant and animal cell. Step 2 Observe the structures present in each. Step 3 Record observations in Table 2.1. Compare the three cell types
Image: Three labelled diagrams side by side โ€” a typical bacterial cell with nucleoid and flagellum, a typical plant cell with cell wall, chloroplast and vacuole, and a typical animal cell with nucleus, mitochondria and lysosomes.
Materials needed
Diagrams of a bacterial cell, a plant cell and an animal cell (Fig. 2.10 a, b and c).
Procedure
1. Study the given diagrams of a bacterial cell, a plant cell and an animal cell.
2. Observe the different structures present in each of them.
3. Record your observations in Table 2.1.
Table 2.1 โ€” Comparison of different kinds of cells based on their structure
S. No. Cell structures Bacterial cell Plant cell Animal cell
1. Cell membrane Present Present Present
2. Cell wall Present Present Absent
3. Cytoplasm Present Present Present
4. Well-defined nucleus (genetic material enclosed by a membrane) Absent Present Present
5. Primitive nucleus (nucleoid) (genetic material without membrane around it) Present Absent Absent
6. Membrane-bound organelles Absent Present Present
Observation
A bacterial cell lacks a well-defined nucleus and membrane-bound organelles. Plant and animal cells have a well-defined nucleus and several membrane-bound organelles.
Explanation
Cells without a well-defined nucleus are called prokaryotic cells. Cells with a well-defined nucleus and membrane-bound organelles are called eukaryotic cells. So the bacterial cell is prokaryotic, while plant and animal cells are eukaryotic.

โ†’ Cells are prokaryotic or eukaryotic.

โ—† Summary
  • Compare three cells.
  • Bacteria: no true nucleus.
  • Plant, animal: true nucleus.
  • So prokaryotic vs eukaryotic.
What are prokaryotic cells?
Prokaryotic Cell Pro primitive Karyon nucleus A cell with no well-defined nucleus or membrane-bound organelles - for example, a bacterial cell.
Image: A bacterial cell shown as a prokaryotic cell with no well-defined nucleus and no membrane-bound organelles, its genetic material lying free in the cytoplasm in the nucleoid region.
Prokaryotic Pro before Karyon Greek: kernel = nucleus A cell that existed before a true nucleus evolved โ€” bacteria are prokaryotic.
  • They lack a well-defined nucleus.
  • They lack membrane-bound organelles.
  • Most activities happen directly in the cytoplasm.
  • "Pro" means primitive and "karyon" means nucleus.
Example: A bacterial cell is a prokaryotic cell.
What are eukaryotic cells?
Eukaryotic Cell Eu true Karyon nucleus A cell with a true, well-defined nucleus and membrane-bound organelles - for example, plant and animal cells.
Eukaryotic Eu Greek: true / good Karyon Greek: kernel = nucleus A cell with a true, well-defined nucleus โ€” plant, animal and fungal cells are eukaryotic.
  • They have a well-defined nucleus.
  • They have several membrane-bound organelles.
  • "Eu" means true and "karyon" means nucleus.
Prokaryotic cell
Eukaryotic cell
Primitive nucleus present.
Primitive nucleus absent.
Diameter 1 to 10 ยตm.
Diameter 10 to 100 ยตm.
Usually unicellular.
Can be unicellular or multicellular.
Membrane-bound organelles absent.
Membrane-bound organelles present.
Membrane-bound nucleus absent.
Membrane-bound nucleus present.
Important Points
  • Most cells have three basic parts: membrane, cytoplasm and nucleus.
  • Organelles are tiny parts inside the cytoplasm, each with a job.
  • Bacterial cells are prokaryotic; plant and animal cells are eukaryotic.
๐Ÿ’ก Ready to Go Beyond
Image: Tiny illustrations of a virus with a protein coat around its genetic material, a viroid as bare genetic material, and a prion as a misfolded protein, all labelled as acellular infectious agents too small for a light microscope.
  • Viruses, viroids and prions are acellular (no cells).
  • They are too small to see under a light microscope.
  • Viruses have genetic material with a protein coat.
  • Viroids lack a protein coat; prions are misfolded proteins.
๐Ÿ’ก Ready to Go Beyond
Image: A eukaryotic cell showing a network of fine fibres called the cytoskeleton crossing the cytoplasm, with small starch grains and crystals of calcium oxalate shown as cell inclusions inside a plant cell.
  • A network of fine fibres forms the cytoskeleton.
  • It gives support, shape and helps internal transport.
  • It is seen only under an electron microscope.
  • Stored starch, calcium oxalate or silica are called cell inclusions.
โ“ Test Yourself
  1. Name the three basic parts of most cells.
    View Answer Hide Answer
    The plasma membrane, the cytoplasm and the nucleus.
  2. What does "prokaryotic" literally mean?
    View Answer Hide Answer
    "Pro" means primitive and "karyon" means nucleus.
  3. Which cell type has membrane-bound organelles?
    View Answer Hide Answer
    The eukaryotic cell.
  4. Is a bacterial cell prokaryotic or eukaryotic?
    View Answer Hide Answer
    Prokaryotic โ€” it has no well-defined nucleus.
  5. Are viruses made of cells?
    View Answer Hide Answer
    No, they are acellular โ€” they have no cells.
Important Definitions
  • Cytoplasm โ€” the semi-fluid, jelly-like substance filling the cell.
  • Organelles โ€” tiny sub-cellular parts in the cytoplasm, each with a special job.
  • Prokaryotic cell โ€” a cell with no well-defined nucleus or membrane-bound organelles.
  • Eukaryotic cell โ€” a cell with a well-defined nucleus and membrane-bound organelles.

๐Ÿ“‹ NCERT Question 9 โ€” Indicate the presence or

Indicate the presence or absence of following structures in bacterial and animal cells: Chromosome, Nucleus, Mitochondria, Golgi complex, Chromoplasts.
View Answer โ†’
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