Chapt_3_Cell_part-3

Plant Cell Water Loss

• Osmosis leads to cell shrinkage when a plant cell loses water; this is known as plasmolysis.

Protoplasm

• Colorless material comprising the living content of a cell, including the nucleus and cytoplasm.
• Contains various organelles responsible for cellular activities.
• Includes cytoplasmic inclusions.

Nucleus

• Discovered by Robert Brown in 1831.
• Double membrane-bound protoplasmic body controlling cellular metabolism and housing genetic information.
• Generally centrally located and spherical.

Structure of the Nucleus

• Nuclear membrane:
  • Double-layered and porous, made of lipids and proteins.
  • Separates nucleus from cytoplasm, providing transparency and density.
• Nucleoplasm:
  • Contains chromatin fibers and nucleoli suspended within; surrounded by nuclear membrane.
• Nucleolus:
  • Spherical and non-membranous; varies in number.
  • Rich in proteins and RNA, and the site for ribosome formation.
• Chromatin material:
  • Thread-like structures containing hereditary material.

Functions of the Nucleus

• Acts as the main control center of the cell.
• Plays a crucial role in cell division.
• Regulates metabolic activities through the action of enzymes.

Chromosomes

• Thread-like structures that tightly package DNA within the nucleus.

Additional Information

• The nucleus is the largest cell structure.
• Human red blood cells (RBCs) and sieve tubes in plants do not contain a nucleus.

Osmosis and Plasmolysis

• Plasmolysis occurs when a plant cell loses water, leading to cell shrinkage or contraction away from the cell wall.

Protoplasm

• Protoplasm is the colorless material that constitutes the living content of a cell.
• It includes essential components like the nucleus and cytoplasm, along with various organelles responsible for cellular activities.
• Cytoplasmic inclusions, which are substances present within the protoplasm, also play roles in cell functions.

Nucleus

• Discovered by Robert Brown in 1831, the nucleus is a double membrane-bound structure that controls cellular metabolism and houses genetic information.
• Acts as the primary control center of the cell, often referred to as the "director."

Structure of the Nucleus

• Nuclear Membrane:
  • Composed of double-layered, porous lipids and proteins, separating the nucleus from the cytoplasm.
• Nucleoplasm:
  • A jelly-like substance that surrounds chromatin fibers and nucleoli, enclosed by the nuclear membrane.
• Nucleolus:
  • Spherical and non-membranous, varies in number and is rich in proteins and RNA; serves as the assembly site for ribosomes.
• Chromatin Material:
  • Comprises thread-like structures called chromatin fibers, containing hereditary material that condenses to form chromosomes.

Function of the Nucleus

• Central role in regulating all cellular activities and metabolic processes controlled by enzymes.
• Major importance in cell division, ensuring proper replication and distribution of genetic material.

Chromosomes

• Chromosomes are tightly packed DNA structures located within the nucleus, critical for genetic inheritance.

Additional Information

• The nucleus is the largest organelle in a typical cell; however, human red blood cells (RBCs) and sieve tubes in plants lack a nucleus.

Plasmolysis

• Occurs when a living plant cell loses water, leading to shrinkage away from the cell wall.
• The process is driven by osmosis.

Protoplasm

• Colourless material containing living contents of the cell, including the nucleus and cytoplasm.
• Contains organelles that perform various cellular activities.
• Substances known as cytoplasmic inclusions are present within protoplasm.

Nucleus

• Discovered by Robert Brown in 1831.
• A double membrane-bound dense protoplasmic structure regulating cellular metabolism and housing genetic information.
• Generally found as a large, spherical body at the center of the cell.

Structure of Nucleus

• Nuclear Membrane
  • Double-layered and porous, composed of lipids and proteins.
  • Distinguishes the nucleus from the cytoplasm and is transparent.
• Nucleoplasm
  • A gel-like substance containing chromatin fibers and nucleoli, surrounded by the nuclear membrane.
• Nucleolus
  • Spherical, non-membranous structure varying in number.
  • Rich in proteins and RNA, functioning as the site for ribosome formation.
• Chromatin Material
  • Composed of fine, thread-like structures called chromatin fibers.
  • Contains hereditary material critical for genetic information.

Function of Nucleus

• Serves as the main control center of the cell.
• Plays a significant role in cellular division.
• Regulates metabolic activities through enzyme management.

Chromosomes

• Thread-like structures located within the nucleus, where DNA is tightly packaged.

Additional Facts

• The nucleus is the largest cell structure.
• Human red blood cells (RBC) and sieve tubes in plants do not have a nucleus.

Functions of Chromosomes

• Chromosomes hold hereditary information responsible for passing traits from one generation to the next.
• DNA within chromosomes provides essential instructions for cellular functions and activities.

Cytoplasm

• The cytoplasm is a living, colorless, semi-liquid substance that fills most of the cell's volume and is in constant motion.
• It is bounded by the cell membrane and consists of specialized organelles that perform various functions.
• Composed of approximately 90% water, with the rest made up of amino acids, vitamins, fats, enzymes, and carbohydrates.
• Cytosol refers to the part of the cytoplasm that excludes organelles, while ergastic bodies are non-living inclusions found in the cytoplasm.

Nucleoid in Bacteria

• In organisms like bacteria, the nuclear region may lack a defined membrane and is termed a nucleoid.
• The nucleoid contains nucleic acids but does not have distinct compartments like eukaryotic cells.

Check Your Concepts - Summary Questions

• Longest cell in the human body: Nerve cells are considered the longest.
• Non-living structure in plant cells: The cell wall is non-living.
• Red blood cells in hypertonic solution: They shrink in size due to water loss.
• Difference between human cheek cells and onion peel cells: The presence of a cell wall in onion peel cells distinguishes them.
• Jelly-like substance within plasma membrane: The cytoplasm is where all organelles float.

Functions of Chromosomes

• Chromosomes are the carriers of hereditary information, crucial for genetics and inheritance.
• DNA within chromosomes encodes instructions necessary for cellular processes and activities.

Cytoplasm

• The cytoplasm is a viscous, semi-liquid substance filling the cell and is continuously in motion.
• It comprises approximately 90% water, with the remaining components including amino acids, vitamins, fats, enzymes, and carbohydrates.
• Specialized organelles essential for cell function are suspended in the cytoplasm.
• Cytosol is the component of cytoplasm that excludes the organelles, consisting of the liquid portion.
• Non-living inclusions known as Ergastic bodies are also present within the cytoplasm.

Nucleoid in Prokaryotes

• In organisms like bacteria, the nuclear region lacks a defined membrane structure, forming a nucleoid that contains nucleic acids.

Concept Checks

• The longest cell type in the human body is nerve cells.
• The non-living structure found in plant cells is the cell wall.
• Red blood cells in a hypertonic solution will shrink in size.
• The main distinction between human cheek cells and onion peel cells is the presence of a cell wall in onion cells.
• The jelly-like substance within the plasma membrane where organelles are suspended is called cytoplasm.

Mitochondria Overview

• Mitochondria were first observed by Köliker and named by Benda in 1898.
• Function as double membrane-bound organelles found in the cytoplasm of eukaryotic cells, present in both plants and animals.

Structure of Mitochondria

• Rod-shaped with an outer membrane that is smooth and porous.
• Inner membrane features finger-like projections called cristae, which increase surface area for metabolic activities.
• Cristae host F1 particles (oxysomes) that contain various respiratory enzymes crucial for energy production.
• Mitochondria possess their own DNA, referred to as mitochondrial DNA.

Functions of Mitochondria

• Key site for cellular respiration, known as the "Powerhouses of the cell," releasing energy for cellular functions.
• Synthesize respiratory enzymes and substances that aid in ATP generation, the energy currency of cells.
• Play a role in regulating calcium ion concentration by storing and releasing calcium as necessary.
• Host the aerobic phase of respiration, specifically the Kreb's cycle, which is vital for energy extraction from nutrients.

Overview of Mitochondria

• First identified by Köliker and named by Benda in 1898.
• Double membrane-bound organelles crucial for eukaryotic cells.

Location

• Present in the cytoplasm of both plant and animal cells.

Structure

• Rod-shaped with a smooth, porous outer membrane.
• Inner membrane features cristae, which are finger-like projections increasing surface area for metabolic processes.
• Cristae contain F1 particles (oxysomes) that bear respiratory enzymes.
• Mitochondria possess their own DNA known as mitochondrial DNA.

Functions of Mitochondria

• Serve as the site for cellular respiration, releasing energy and earning the title "Powerhouses of the cell."
• Energy produced is utilized for various cellular functions.
• Synthesize specialized respiratory enzymes that facilitate ATP generation.
• Regulate calcium ion concentration through storage and release based on cellular needs.
• Host the aerobic portion of respiration known as the Krebs cycle.