1.4 Ultrastructure of Animal and Plant Cells

Introduction

The cell is the basic unit of life. When we study the cell in detail, we need to see its fine internal structure. This fine structure can only be seen with an electron microscope. The detailed structure of a cell, including all its organelles and membranes, is called its ultrastructure.

Definition

Ultrastructure is the fine structure of the cell as seen with the electron microscope.

In simple words: Ultrastructure means the very detailed internal structure of a cell that can only be seen with a powerful electron microscope.

Core Concept

• The cell is not just a simple bag of fluid.
• Inside the cell, there are many specialized structures called organelles.
• Each organelle has a specific structure and function.
• The ultrastructure of a cell includes:
• The cell membrane (plasma membrane)
• The cytoplasm
• The nucleus and its parts
• Various membrane-bound organelles
• Non-membranous structures like ribosomes and centrioles

Detailed Explanation

Ultrastructure of an Animal Cell

An animal cell contains the following structures:

Ultrastructure of a Plant Cell

A plant cell contains the following structures:

Key Differences Between Animal and Plant Cells

Intermediate Level

The ultrastructure of a cell reveals that it is highly organized. Each organelle has a specific structure that allows it to perform its function efficiently.

• The cell wall is made of cellulose.
• It provides support and protection.
• It maintains the shape of the cell.
• It prevents excessive uptake of water.

• Chloroplasts contain chlorophyll.
• They are the site of photosynthesis.
• They allow plants to make their own food using sunlight, carbon dioxide, and water.

• It stores water, nutrients, and waste.
• It helps maintain turgor pressure (keeps the cell firm).
• It provides mechanical support to the plant.

• Centrioles help in cell division.
• They form the spindle fibres that separate chromosomes during mitosis.

• Lysosomes contain digestive enzymes.
• In animal cells, they break down waste and worn-out organelles.
• In plant cells, the large central vacuole performs similar functions.

Important Points

• 1. Ultrastructure is the fine structure of the cell as seen with an electron microscope.
• 2. Animal cells contain: cell membrane, cytoplasm, nucleus, nucleolus, chromatin, mitochondria, RER, SER, ribosomes, Golgi apparatus, Golgi vesicles, lysosomes, peroxisomes, vacuoles, centrosome, microtubules.
• 3. Plant cells contain: cell wall, cell membrane, cytoplasm, nucleus, nucleolus, RER, SER, ribosomes, Golgi bodies, Golgi vesicles, large central vacuole, tonoplast, mitochondria, chloroplast, intermediate filaments, microtubules.
• 4. Key differences between animal and plant cells:
• - Cell wall: present in plant cells, absent in animal cells.
• - Chloroplast: present in plant cells, absent in animal cells.
• - Large central vacuole: present in plant cells, absent in animal cells.
• - Centrioles: present in animal cells, usually absent in plant cells.
• - Lysosomes: present in animal cells, rare in plant cells.
• 5. Organelles by membrane type:
• - Single membrane: lysosomes, peroxisomes, vacuoles, vesicles, Golgi, ER.
• - Double membrane: nucleus, mitochondria, chloroplast.
• - No membrane: ribosomes, centrioles.
• 6. Ultrastructure is related to function: Different cells have different amounts of organelles depending on their function.

Remember

• - Ultrastructure = fine structure of cell (electron microscope)
• - Animal cell: cell membrane, cytoplasm, nucleus, nucleolus, chromatin, mitochondria, RER, SER, ribosomes, Golgi, vesicles, lysosomes, peroxisomes, vacuoles, centrosome, microtubules
• - Plant cell: cell wall, cell membrane, cytoplasm, nucleus, nucleolus, RER, SER, ribosomes, Golgi, vesicles, large central vacuole, tonoplast, mitochondria, chloroplast, intermediate filaments, microtubules
• - Plant cell extra: cell wall, chloroplast, large central vacuole
• - Animal cell extra: centrioles, lysosomes (usually)
• - Single membrane: lysosomes, peroxisomes, vacuoles, vesicles, Golgi, ER
• - Double membrane: nucleus, mitochondria, chloroplast
• - No membrane: ribosomes, centrioles
• - Ultrastructure → function

Common Mistakes

• 1. Thinking animal cells have a cell wall – Animal cells do not have a cell wall. They only have a cell membrane.
• 2. Thinking plant cells have centrioles – Plant cells usually do not have centrioles.
• 3. Confusing the large central vacuole with small vacuoles – Plant cells have a large central vacuole; animal cells may have small, temporary vacuoles.
• 4. Forgetting that chloroplasts are only in plant cells – Animal cells do not have chloroplasts.
• 5. Mixing up single and double membrane organelles – Nucleus, mitochondria, and chloroplast have double membranes; lysosomes, peroxisomes, vacuoles, and vesicles have single membranes.
• 6. Thinking ribosomes are membrane-bound – Ribosomes have no membrane.
• 7. Forgetting the tonoplast – The tonoplast is the membrane surrounding the vacuole in plant cells.
• 8. Confusing chromatin and chromosomes – Chromatin is the thread-like material in the nucleus; chromosomes are condensed chromatin visible during cell division.
• 9. Thinking all cells have the same number of organelles – The number and type of organelles vary depending on the cell's function.

Quick Revision

• Ultrastructure is the fine structure of the cell as seen with an electron microscope.
• Animal cell structures: cell membrane, cytoplasm, nucleus, nucleolus, chromatin, mitochondria, RER, SER, ribosomes, Golgi apparatus, Golgi vesicles, lysosomes, peroxisomes, vacuoles, centrosome, microtubules.
• Plant cell structures: cell wall, cell membrane, cytoplasm, nucleus, nucleolus, RER, SER, ribosomes, Golgi bodies, Golgi vesicles, large central vacuole, tonoplast, mitochondria, chloroplast, intermediate filaments, microtubules.
• Key differences:
• Cell wall: plant only
• Chloroplast: plant only
• Large central vacuole: plant only
• Centrioles: animal only (usually)
• Lysosomes: animal only (usually)
• Organelles by membrane:
• Single: lysosomes, peroxisomes, vacuoles, vesicles, Golgi, ER
• Double: nucleus, mitochondria, chloroplast
• None: ribosomes, centrioles
• Ultrastructure is related to function – different cells have different amounts of organelles.

60-Second Revision

• Ultrastructure = fine structure of cell (electron microscope)
• Animal cell: cell membrane, cytoplasm, nucleus, nucleolus, chromatin, mitochondria, RER, SER, ribosomes, Golgi, vesicles, lysosomes, peroxisomes, vacuoles, centrosome, microtubules
• Plant cell: cell wall, cell membrane, cytoplasm, nucleus, nucleolus, RER, SER, ribosomes, Golgi, vesicles, large central vacuole, tonoplast, mitochondria, chloroplast, intermediate filaments, microtubules
• Plant cell extra: cell wall, chloroplast, large central vacuole
• Animal cell extra: centrioles, lysosomes
• Single membrane: lysosomes, peroxisomes, vacuoles, vesicles, Golgi, ER
• Double membrane: nucleus, mitochondria, chloroplast
• No membrane: ribosomes, centrioles
• Warning: Animal cells do not have a cell wall. Plant cells usually do not have centrioles. Chloroplasts are only in plant cells. Ribosomes have no membrane.