Cell Biology Concepts

Basic Unit of Life

• In 1665, Robert Hooke examined a cork section under a microscope
• Hooke saw structures resembling chambers in a beehive, and named them cells
• Schleiden, Schwann, and Rudolf Virchow introduced the cell theory
• The cell theory states:
• The cell is the structural and functional unit of life
• All organisms consist of one or more cells
• New cells originate from pre-existing cells

Concept of the Cell

• A cell represents the most basic structural unit in the organization of a living body
• Organisms with a single cell are unicellular
• Organisms with numerous cells are multicellular
• Cells each perform different functions within the body

Structure of Cells

• Oxygen is carried by red blood cells
• Nerve impulses are transmitted by neurons
• A cell is the smallest biological unit adapted to performing a specific function
• Cells vary in shape, size, and function
• Most cells are not visible without a light microscope

Studying Cells

• Cheek cells are used to study animal cells
• Onion epidermal cells are used to study plant cells
• To prepare animal cells for viewing:
• Scrape inside of the cheek lining using a spoon
• Transfer to a slide with water and cover with a coverslip, while avoiding air bubbles
• Observe under a light microscope
• To prepare plant cells for viewing:
• Cut an onion and get a fleshy inner tissue
• Remove peel, transfer to watch glass with water
• Put a water drop on a slide
• Transfer the specimen and cover with a coverslip, while avoiding air bubbles
• Observe it through the microscope

Typical Cell

• Small structures within a cell performing various functions are called organelles
• Organelle types and quantities differ based on the cell's function
• Organelles are known as a typical cell
• Cells with a specific set of organelles can be found in living organisms
• The animal cell contains:
• Cell membrane
• Cytoplasm
• Nucleus
• The plant cell contains:
• Cell membrane
• Cytoplasm
• Nucleus
• Cell wall
• Vacuole

Cell Components

• All animal cells have a plasma (cell) membrane
• It’s semi-permeable and selectively permeable
• Cell have a centralized nucleus
• Cytoplasm is gelatinous
• Plant cell outer covering is the cell wall, made of cellulose
• Inside the cell wall is the plasma membrane
• A large vacuole is at the plant cell's center
• Unlike plant cells, animal cells generally do not have vacuoles
• Animal and plant cells contain different organelles performing different functions
• Most organelles can't be seen using a light microscope, so an electron microscope is necessary

Animal vs Plant Cells

• Animal cells lack a cell wall, while plant cells have one
• Animal cells have a large content of cytoplasm
• Plant cells have cytoplasm pushed towards the periphery
• Animal cells lack a large vacuole, but sometimes have small ones
• Plant cells have a large central vacuole, or a few vacuoles
• Animal cells lack chloroplasts
• Plant cells contain chloroplasts

Cell Organelles and Structures

• Each organelle and structure in a cell has a specific function
• This divides labor within the cell

Cell Wall

• The outermost covering of a plant cell is the cell wall
• A dead structure made of cellulose
• Its main functions include maintaining cell shape, providing support, and protection

Plasma Membrane (Cell Membrane)

• In plant cells, the plasma membrane is located inside the cell wall
• In animal cells, it forms the cell boundary
• It consists of phospholipids and proteins, acting as a semi-permeable barrier
• Main functions include enclosing the cell, allowing water and ion entry, and controlling material flow
• The plasma membrane is also known as the cell membrane

Cytoplasm

• The cytoplasm is the gelatinous liquid portion of the cell, excluding organelles
• Inorganic and organic substances are present in it
• Its functions include maintaining cell shape, housing organelles, and allowing metabolic processes
• Structures submerged in the cytoplasm are called organelles
• Mitochondria
• Nucleus
• Endoplasmic reticulum
• Golgi complex

Nucleus

• The nucleus is the primary organelle of the cell, enclosed by a nuclear envelope
• It contains one or two nucleoli and the chromatin body inside
• During cell division, the chromatin body turns into chromosomes
• Chromosomes store genetic material and transfer inherited traits

Chromosomes

• The number of chromosomes varies by species
• Humans have 46 chromosomes, frogs have 26, and paddy plants have 24
• The nucleus's main job is to control the cell's functions

Mitochondrion

• Oval or rod-shaped organelle with a membrane
• Aerobic respiratory reactions take place within it
• Releases energy
• It is known as the cell's power house
• The energy is used for the activities of the cell

Golgi Complex

• A stack of membrane-bound sacs with secretory vesicles
• Production of secretory substances, packaging, and secretion

Ribosome

• Small organelle without a membrane, made of large and small subunits
• They can be found freely in the cytoplasm or attached to the Endoplasmic Reticulum
• Its function is to provide a place for protein synthesis

Endoplasmic Reticulum

• Inter-membranous network of flat or tubular sacs within the cytoplasm.
• Two types:
• Rough Endoplasmic Reticulum (RER):
• Rough due to ribosomes attached to the membrane
• Transports proteins within the cell
• Smooth Endoplasmic Reticulum (SER):
• Network of tubular sacs lacking ribosomes
• Synthesizes lipids and steroids

Vacuole

• A fluid-filled organelle in plant cells, surrounded by a membrane (tonoplast)
• The fluid inside is called cell sap, containing water, sugar, ions, and pigments
• Vacuoles store water, sugar, ions, and pigments within the cell
• Animal cells generally lack vacuoles, though small vacuoles may be present sometimes
• Contractile vacuoles are found in unicellular organisms
• Its functions are to maintain water balance, provide support, and give color

Cell Growth

• A key characteristic of organisms, defined as an irreversible increase in size or dry mass
• A cell has a maximum growth limit.
• Beyond this limit it doesn't develop

Cell Division

• Cells can divide by a method in order to grow and create multiply, forming new cells
• Cell division is when cellular material is divided
• To split a eukaryotic cell, split the nucleus, then the cytoplasm
• Genetic are transferred from one cell to the next using chromosomes generation
• Chromosomes can be seen easily during cell division

Chromosomes in Somatic Cells

• The usual number of chromosomes for a species somatic cell is set in stone
• Human somatic cells have 46
• This consists of 23 pairs of chromosomes with hereditary details
• Chromosome pairs that contain the same hereditary information called homologous pairs One homologous chromosome inherited from eachparent
• Therefore kids gain 46 chromosomes with 23 received for each parent

Cell Division Methods

• Cell division takes place in 2 ways
• Mitosis
• Meiosis

Mitosis

• Cell division which multiplies the number of cells by maintaining a constant number of chromosomes in cells
• The nucleus divides first, then the produces two cells with the same qualities

Significance of Mitosis

• Growth in multicellular organisms
• Asexual reproduction technique
• Wound healing and replacing cells

Meiosis

• Cell division that halves the number of chromosomes
• During creation of gametes, meiosis will take action
• Chromosomes should be halved to create gametes that are haploid
• For fertilization, it creates zygotes

Stages of Meiosis

• Meiosis occurs in two stages
• The first stage is meiotic division, with one mitosis after

Meiosis Significance

• Keeps the number of chromosomes constant throughout cell division
• Mutation can occur from structural chromosome changes which causes evolution
• Variation in chromosomes can occur during meiosis which fuels diversity in offspring

Differences Between Meiosis and Mitosis

• Mitosis - One division, Meiosis - Two divisions
• Mitosis - Occurs only in diploid cells, Meiosis - Occurs in diploid and haploid cells
• Chromosome variations and changes occur in Meiosis
• Chromosomes rarely change in Mitosis
• Meiosis creates four daughter cells, Mitosis creates two
• Meiosis creates a chromosome cell half the number of the parent, Mitosis is the same
• Daughter cells are different for Meiosis, and similar for Mitosis

Explore essential cell biology concepts, including organelle functions like the smooth endoplasmic reticulum, cell division, and the cell theory. Understand the importance of structures such as vacuoles and neurons. Learn about microscope techniques and their impact on cell observation.