BIO 111 (BASIC PRINCIPLES OF BIOLOG AND CELL BIOLOGY)
CONCEPT OF SCIENCE
The word “Science” comes from the Latin word “Scientia”, which means knowing something. It observes and understands everything that take place around us. Science is the systematic study of the natural and physical world through observation and experimentation. It is based on the idea that the natural world is governed by laws that can be discovered and understood through careful observation and testing. Science also helps us to better understand the world around us and our place in it. Science is a way of learning about the world around us by asking questions and doing experiments.
HISTORY OF SCIENCE
The history of science is the development of science over time. Science's earliest roots can be traced to Ancient Egypt around 3000 to 1200 BCE. These civilizations' contributions to mathematics, astronomy, and medicine influenced later Greek natural philosophy of classical antiquity, wherein formal attempts were made to provide explanations of events in the physical world based on natural causes. The ancient Greeks made significant advances in science, including the development of geometry, trigonometry, and physics. They also developed the scientific method, a process of using observation and experimentation to test hypotheses. Some of the most famous Greek scientists include Pythagoras, Euclid, Archimedes, and Aristotle. Science flourished during the Islamic Golden Age (8th to 13th centuries), when Muslim scholars made significant contributions to mathematics, astronomy, chemistry, and medicine. They also developed new scientific instruments, such as the astrolabe and the quadrant. Some of the most famous Muslim scientists include Ibn Sina (Avicenna), Ibn Rushd (Averroes), and Al-Khwarizmi. Science in Europe began to flourish during the Renaissance (14th to 17th centuries). This was a time of great intellectual and cultural advancement, and many new scientific discoveries were made. Some of the most famous scientists of the Renaissance include Nicolaus Copernicus, Galileo Galilei, and Johannes Kepler. The Scientific Revolution (16th to 18th centuries) was a period of rapid and dramatic change in science. During this time, the scientific method was refined and used to make many new discoveries, including the laws of motion, the laws of gravity, and the discovery of calculus. Some of the most famous scientists of the Scientific Revolution include Isaac Newton, Gottfried Wilhelm Leibniz, and René Descartes. The 19th and 20th centuries saw even more rapid advances in science and technology. Some of the most important scientific discoveries of this period include the development of the theory of evolution, the discovery of the atom, and the development of quantum mechanics.
IMPORTANCE OF SCIENCE
Science is important because it helps us to understand the world around us and to solve problems.
Science helps us to understand the natural world. It teaches us about the biology of living things.
Science helps us to solve problems, to think critically and to design experiments to test our hypotheses.
Science improves our quality of life, which lead to the development of new technologies that make our lives easy, such as computers and smartphones.
It teaches us about the universe and our place in it. It helps us to develop a sense of wonder and curiosity about the world around us.
It support scientific research and education so that we can continue to make progress and solve the challenges of the future.
SCIENTIFIC METHOD
The scientific method is a process for experimentation that is used to explore observations and answer questions. It is a cyclical process that involves making observations, forming hypotheses, testing those hypotheses, and drawing conclusions.
The scientific method can be broken down into the following steps:
Make an observation. This is the first step in the scientific method, and it involves noticing something in the world around you that you find interesting.
Ask a question. Once you have made an observation, you can start to ask questions about it. For example, if you observe that plants grow better when they are watered regularly, you might ask the question, "What is the effect of water on plant growth?"
Do some research; before you start testing any hypotheses, it is important to do some research to learn what is already known about the topic. This will help you to develop a more informed hypothesis and to design a better experiment.
Form a hypothesis. A hypothesis is a proposed explanation for your observation. It is a testable statement that predicts what will happen under certain conditions. For example, your hypothesis about the effect of water on plant growth might be, "Plants that are watered regularly will grow taller than plants that are not watered regularly."
Design an experiment. An experiment is a test of your hypothesis. It is important to design your experiment carefully so that you can get reliable results.
Conduct the experiment. Once you have designed your experiment, you can start conducting it. Be sure to follow your procedure carefully and to record all of your data.
Analyze the data. Once you have collected your data, you need to analyze it to see if it supports your hypothesis. This may involve using statistical tests or simply looking at the trends in your data.
Draw a conclusion. Based on your analysis of the data, you can now draw a conclusion about your hypothesis. If your data supports your hypothesis, then you can accept it. If your data does not support your hypothesis, then you need to reject it and come up with a new hypothesis.
Communicate your results. Once you have drawn a conclusion, you should communicate your results to others. This can be done by writing a scientific paper, giving a presentation, or simply talking to people about your work.
CONCEPT OF BIOLOGY
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. Biology is the science of life. It spans multiple levels from smaller cells to organisms and populations.
BRANCHES OF BIOLOGY
Biology is a complex subject, but it can be broadly divided into several major branches:
Molecular biology: The study of the molecules that make up living organisms and how they interact with each other.
Cell biology: The study of the structure, function, and behavior of cells.
Genetics: The study of genes and heredity.
Evolution: The study of how species change over time.
Biochemistry: The study of the chemical processes that occur in living organisms.
Microbiology: The study of microorganisms, such as bacteria and viruses.
Botany: The study of plants.
Zoology: The study of animals.
Physiology: The study of the functions of living organisms.
Ecology: The study of the interactions between organisms and their environment.
RELATION OF BIOLGY TO OTHER SUBJECTS
Biology is related to many other science subjects, including chemistry, physics, mathematics, computer science, medicine, agriculture and environmental sciences.
Chemistry: Biology and chemistry are closely related because all living things are made up of chemicals and chemical reactions and are essential for life. Biologists use chemistry to understand the structure and function of biological molecules, such as DNA, proteins, and carbohydrates. They also use chemistry to develop new drugs and treatments for diseases.
Physics: Biology and physics are related because the laws of physics apply to all living things. For example, biologists use physics to understand how muscles work, how blood flows through the body, and how plants grow towards the light. They also use physics to develop new medical technologies.
Mathematics: Biology and mathematics are related because biologists use mathematics to analyze data and develop models of biological systems. For example, biologists use mathematics to study the spread of diseases, the population dynamics of animal species, and the evolution of living things.
Computer science: Biology and computer science are related because biologists use computers to store, analyze, and model biological data. For example, biologists use computers to sequence DNA, map the human genome, and develop new drugs.
Medicine: Biologists work with doctors and other medical professionals to develop new drugs and treatments for diseases. They also study the human body to learn how to prevent diseases and improve human health.
Agriculture: Biologists work with farmers and other agricultural professionals to develop new crops and livestock that are more productive and resistant to pests and diseases. They also study the environment to develop sustainable agricultural practices.
Environmental science: Biologists work with environmental scientists to study the natural world and to develop strategies for protecting the environment and the biodiversity that it supports. They also study the impact of human activities on the environment.
PRINCIPLES OF CLASSIFICATION
The principle of classification in biology is to group organisms together based on their common characteristics. These characteristics can be physical, such as body structure and morphology, or behavioral, such as feeding habits and social interactions. Biologists also consider the evolutionary relationships between organisms when classifying them. The most important principle in biological classification is monophyly. A monophyletic group is a group that includes all of the descendants of a common ancestor and no other organisms. For example, the class Mammalia is monophyletic because it includes all of the descendants of a common ancestor that lived about 200 million years ago. Another important principle in biological classification is hierarchy. Organisms are classified into a hierarchy of groups, with each group nested within a larger group. The most basic taxonomic group is the species. Species are groups of organisms that can interbreed and produce viable offspring. Species are grouped together into genera, genera are grouped together into families, and so on. The highest taxonomic group is the domain.
The following are some examples of how the principles of classification are used in biology:
All organisms that have a backbone are classified into the phylum Chordata. This includes mammals, birds, reptiles, amphibians, and fish.
All organisms that have feathers are classified into the class Aves. This includes all birds.
All organisms that have flowers and produce seeds are classified into the division Angiospermae. This includes all flowering plants.
By grouping organisms together based on their shared characteristics, biologists can learn more about their evolution, their relationships to each other, and their roles in the environment.
HISTORY OF CLASSIFICATION
The history of classification can be traced back to ancient times. Early human classified things like plants and animals based on their physical characteristics and how they could be used. For example, plants might be classified as edible or poisonous, and animals might be classified as dangerous or safe to eat. One of the first major classification systems was developed by the Greek philosopher Aristotle in the 4th century BC. Aristotle classified all living things into two kingdoms: plants and animals. He then further classified animals into different groups based on their physical characteristics, such as whether they had blood, lungs, or feathers. In the 18th century, the Swedish botanist Carl Linnaeus developed a hierarchical classification system for all living things. Linnaeus's system is based on the physical characteristics of organisms, and it is still used today. Since Linnaeus's time, scientists have developed more sophisticated classification systems that take into account evolutionary relationships between organisms.
Here are some key events in the history of classification:
4th century BC: Aristotle develops a classification system for all living things.
18th century: Carl Linnaeus develops a hierarchical classification system for all living things.
20th century: Robert Whittaker proposes a five-kingdom classification system.
21st century: Scientists continue to develop new classification systems that take into account new discoveries about the natural world.
TAXONOMY
Taxonomy in biology is the science of naming, defining, and classifying groups of biological organisms based on shared characteristics. It is a fundamental part of biology, as it allows scientists to organize their knowledge of the living world and to understand the relationships between different organisms. Taxonomists group organisms together into a hierarchy of groups, with each group nested within a larger group. The most basic taxonomic group is the species.
Here is an example of a taxonomic hierarchy for a human:
Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Genus: Homo
Species: Homo sapiens
NOMENCLATURE
Nomenclature is the system of naming organisms. It is governed by a set of rules and conventions that ensure that each organism has a unique and unambiguous name. The most widely used system of nomenclature is the Linnaean system, which uses a two-word Latin name for each species. The first word is the genus name, and the second word is the species epithet. In science, nomenclature is used to name organisms, chemical compounds, and other scientific concepts. For example, the scientific name for the human species is Homo sapiens. The chemical formula for water is H2O.Nomenclature systems are important because they help us to avoid confusion and to communicate with each other about complex topics in a clear and concise way. For example, if we all used different names for the same things, it would be very difficult to understand each other.
Nomenclature systems are often complex and have a long history. For example, the scientific nomenclature system for organisms was developed by the Swedish botanist Carl Linnaeus in the 18th century. Linnaeus's system is based on the Latin language, and it is still used today by scientists all over the world.
FIVE (5) KINGDOM SYSTEM OF CLASSIFICATION
The five kingdom system of classification is a useful tool for organizing and understanding the diversity of life on Earth. It is still widely used today, although some scientists have proposed more recent classification systems that take into account new discoveries about the evolutionary relationships between different organisms. The five kingdom system of classification was proposed by Robert Whittaker in 1969. It is a hierarchical system that classifies all living things into five kingdoms. This classification system is based on a number of factors, including cell type, cell structure, mode of nutrition, and reproductive strategy.
The table below summarizes the key characteristics of each kingdom:
KINGDOM
CELL TYPE
CELL STRUCTURE
MODE OF NUTRITION
REPRODUCTIVE STRATEGY
monera
Prokaryotic
No nucleus or membrane-bound organelles
Autotrophic or heterotrophic
Asexual or sexual
protista
Eukaryotic
Unicellular, with a nucleus and membrane-bound organelles
Autotrophic, heterotrophic or both
Asexual or sexual
Fungi
Eukaryotic
Multicellular, with a nucleus and membrane-bound organelles
Heterotrophic
Asexual or sexual
Plantae
Eukaryotic
Multicellular, with a nucleus and membrane-bound organelles
Autotrophic
Asexual or sexual
Animalia
Eukaryotic
Multicellular, with a nucleus and membrane-bound organelles
Heterotrophic
Sexual
Kingdoms are divided into subgroups at various levels. The following flowchart shows the hierarchy of classification.
GENERAL CHARACTERISTICS OF LIVING AND NON-LIVING THINGS
Following are the important characteristics of living things:
MOVEMENT: - Living things exhibit locomotory motion, they move. Animals are able to move as they possess specialized locomotory organs, for example – Earthworms move through the soil surface through longitudinal and circular muscles. Plants move in order to catch sunlight for photosynthesis
RESPIRATION: -Living things respire. Respiration is a chemical reaction, which occurs inside cells to release energy from the food. Transport of gases takes place. The food that is ingested through the process of digestion is broken down to release energy that is utilized by the body to produce water and carbon dioxide as by-products.
NUTRITION: - They acquire and fulfil their nutritional requirements to survive through the process of nutrition and digestion, which involves engulfing and digesting the food. Some living organisms are also autotrophic, which means they can harness the sun’s energy to make their food (also known as autotrophs).
IRRITABILITY: - Living things are sensitive to touch (and other stimuli as well) and have the capability to sense changes in their environment. Eg. Sweating when it is hot.
GROWTH: - Living things mature and grow through different stages of development.
EXCRETION: - Excretion is the process of removing waste products from the body. These waste products can be toxic to the cells and tissues of the organism if they are allowed to accumulate. All living things excrete, but the way they do it varies depending on the organism.
REPRODUCTION: - One of the striking features is that living things are capable of producing offspring of their own kind through the process of reproduction, wherein genetic information is passed from the parents to the offspring.
DEATH: - Death is a natural part of life, and it is something that all living things will experience at some point. However, it is also a difficult and emotional topic, and it is often hard to talk about. Death is the end of life on earth.
NB: there are some gray areas between living and non-living things. For example, viruses are considered to be non-living because they cannot reproduce on their own. However, they do contain DNA or RNA, which is a characteristic of living things.
CONCEPT OF CELL BIOLOGY
Cell biology, also known as cellular biology or cytology, is the study of the structure, function, and behavior of cells. Cell biology is based on the cell theory, which states that all living organisms are composed of one or more cells, and that the cell is the basic structural and functional unit of life. Cell biology research is essential for understanding the basic processes of life, such as growth, development, reproduction, and disease. It also has important applications in medicine, agriculture, and other fields. Cell biology is a rapidly evolving field, and new discoveries are being made all the time. Researchers are using increasingly sophisticated tools and techniques to study cells in detail, and they are learning more and more about how cells work and how they interact with each other.
DEFINITION OF CELL
A cell is the basic unit of life. All living things are made up of cells, either one cell (unicellular organisms) or many cells (multicellular organisms). Cells are tiny structures, but they are very complex and perform many important functions, such as:
Structure: Cells provide structure and support for living things.
Metabolism: Cells convert food into energy and synthesize new molecules.
Reproduction: Cells can divide to create new cells.
Growth and development: Cells can grow and develop to form new tissues and organs.
Response to stimuli: Cells can respond to changes in their environment.
Cells are enclosed by a thin, flexible membrane that protects the cell's contents and regulates what goes in and out of the cell. Inside the cell, there is a jelly-like substance called cytoplasm. The cytoplasm contains many different cell organelles, which are structures that perform specific functions within the cell. The most important cell organelle is the nucleus. The nucleus contains the cell's DNA, which is the genetic material that determines the cell's characteristics and functions. Other important cell organelles include the mitochondria, which produce energy for the cell, and the ribosomes, which synthesize proteins.
Cells can be divided into two main types: prokaryotic and eukaryotic cells. Prokaryotic cells are simpler and smaller than eukaryotic cells. They do not have a nucleus or other membrane-bound organelles. Eukaryotic cells have a nucleus and other membrane-bound organelles. Prokaryotic cells are found in single-celled organisms, such as bacteria and archaea. Eukaryotic cells are found in all other living things, including plants, animals, fungi, and protists. Cells are amazing structures that are essential for life. By understanding the structure and function of cells, we can better understand how living things work
HISTORY OF CELL AND CELL THEORY
In 1665, Robert Hooke published his book Micrographia, which included drawings and descriptions of the microscopic world he had observed with his compound microscope. One of his most famous observations was of a thin slice of cork, which he described as being made up of "little boxes" or "cells." This was the first time that anyone had observed cells, but Hooke did not fully realize their significance. Over the next century, other scientists made further observations of cells, using increasingly powerful microscopes. In 1672, Antoni van Leeuwenhoek described the first living cells, which he observed in rainwater and pond scum. He called these tiny organisms "animalcules."
Cell theory
In the early 1800s, scientists began to develop a more comprehensive understanding of cells. In 1838, German scientists Theodor Schwann and Matthias Jakob Schleiden proposed the cell theory, which states that:
All living things are made up of one or more cells.
The cell is the basic unit of structure and function in living things.
All cells come from pre-existing cells.
The cell theory was a major breakthrough in biology, as it provided a unifying framework for understanding all living things.
Later in the years since Schwann and Schleiden proposed the cell theory, scientists have made many new discoveries about cells. For example, they have discovered that cells are much more complex than Schwann and Schleiden imagined. They have also discovered that there are many different types of cells, each with its own specialized function.
Today, the cell theory is one of the most fundamental principles of biology. It is essential for understanding how living things work and how they evolve.
GENERALISED ANIMAL CELL
GENERALISED PLANT CELL
Difference between generalized animal and plant cell structures:
Difference between Animal and Plant cell
Animal Cell
Plant cell
It does not have a cell wall.
It consists of a cellulose cell wall outside the cell membrane.
Are irregular or round in shape.
Are square or rectangular in shape.
Centrosomes and centrioles are present.
Centrosomes and centrioles are absent.
Plastids are absent
Plastids are present.
Vacuoles are usually small and sometimes they are absent.
Vacuoles are few large or single and centrally positioned vacuole.
Cilia is present in most animal cells.
Cilia is absent
Mitochondria is present and numerous in number.
Mitochondria is present but fewer in number
The mode of nutrition is heterotrophic.
The mode of nutrition is primarily autotrophic.
Single highly complex and prominent Golgi apparatus is present.
Many simpler units of Golgi apparatus called dictyosomes are present.
Similarities between animal and plant cell
1. Both have a cell membrane or plasma membrane.
2. Both have ribosomes.
3. Both have endoplasmic reticulum.
4. Both possess a well-defined nucleus and cytoplasm. Genetic material DNA is also surrounded by a nuclear membrane.
FUCTION OF THE CELL ORGANELLES
Nucleus: The nucleus is the control center of the cell. It contains the cell's DNA, which is the genetic material that determines the cell's structure and function.
Mitochondria: The mitochondria are the powerhouses of the cell. They produce energy for the cell by breaking down food molecules.
Ribosomes: The ribosomes are the protein factories of the cell. They produce proteins, which are essential for all cell functions.
Endoplasmic reticulum (ER): The ER is a transport system within the cell. It transports proteins and other molecules throughout the cell.
Golgi apparatus: The Golgi apparatus is a packaging and sorting center within the cell. It packages and sorts’ proteins and other molecules for transport to other parts of the cell or for secretion outside the cell.
Lysosomes: The lysosomes are the digestive system of the cell. They break down waste products and other unwanted materials within the cell.
Vacuole: The vacuole is a storage compartment within the cell. It stores water, nutrients, and other molecules.
Cell wall: The cell wall is a rigid structure that surrounds the cell membrane of plant cells. It provides support and protection for the cell.
Cell membrane: The cell membrane is a thin, flexible barrier that surrounds the cell. It protects the cell from its environment and regulates the movement of molecules into and out of the cell.
Centrosomes: The centrosomes are organelles that help to organize cell division. They contain two structures called centrioles, which help to separate the chromosomes during mitosis and meiosis.
Chromosomes are thread-like structures found in the nucleus of cells. They contain genes, which are the units of heredity. Genes are made up of DNA, which is the genetic material of the cell. DNA contains the instructions for building and maintaining the cell. Chromosomes carry genetic information from one generation to the next and regulate gene expression.
Chloroplasts: Chloroplasts are green plastids that contain chlorophyll, the pigment that absorbs sunlight. Chloroplasts are responsible for photosynthesis. Plastids are organelles found in the cells of plants and algae. Photosynthesis, the process by which plants use sunlight to convert carbon dioxide and water into oxygen and glucose.
CHEMICAL CONSTITUENT OF CELL
The chemical constituents of cells can be divided into two main categories: inorganic and organic.
Inorganic constituents
Inorganic constituents make up about 1% of the mass of a cell. They include water, salts, and minerals.
Water: Water is the most abundant inorganic constituent in cells, accounting for about 70% of the cell's mass. Water is essential for all cell functions, including transport, metabolism, and cell signaling.
Salts: Salts are inorganic compounds that are made up of ions. The most common salts in cells are sodium chloride (NaCl) and potassium chloride (KCl). Salts play a role in maintaining the cell's fluid balance and electrical charge.
Minerals: Minerals are inorganic elements that are essential for cell function. Some important minerals in cells include calcium, magnesium, iron, and zinc.
Organic constituents
Organic constituents make up about 99% of the mass of a cell. They include carbohydrates, proteins, lipids, and nucleic acids.
Carbohydrates: Carbohydrates are organic molecules that are made up of carbon, hydrogen, and oxygen. They are the main source of energy for cells. Carbohydrates are also used to build cell structures, such as the cell wall and cell membrane.
Proteins: Proteins are organic molecules that are made up of carbon, hydrogen, oxygen, and nitrogen. They are essential for all cell functions, including metabolism, cell signaling, and structural support.
Lipids: Lipids are organic molecules that are made up of carbon, hydrogen, and oxygen. They are the main source of energy storage for cells. Lipids are also used to build cell membranes and other cell structures.
Nucleic acids: Nucleic acids are organic molecules that are made up of carbon, hydrogen, oxygen, nitrogen, and phosphorus. They are the genetic material of the cell. Nucleic acids contain the instructions for building and maintaining the cell.
These are just a few of the many chemical constituents of cells. Cells are complex and dynamic structures, and scientists are still learning new things about them all the time.
PHYSICAL PROCESSES IN THE CELL
Physical processes in the cell are the fundamental processes that underlie all cellular activities. They include the movement of molecules across membranes, the transport of materials within the cell, and the conversion of energy from one form to another. Physical process in the cell involve movement of materials in and out of a cell, both these movement involve movement along the concentration gradient. Before looking at the detailed description of the processes we have to look at the following;
PARTICLE SIZE: particle size is an important factor in cell biology that can affect the ability of particles to enter, move within, and interact with cells. This understanding of particle-cell interactions is essential for the development of new biomedical technologies that use nanoparticles to deliver drugs, genes, and other therapeutic agents to cells.
Molecules are neutral particles made of two or more atoms bonded together. The atoms in a molecule can be the same type of atom, or they can be different types of atoms. For example, the molecule of water (H2O) is made up of two hydrogen atoms and one oxygen atom. Molecules are the most common type of particle found in nature, and they make up all of the living things on Earth.
Ions are atoms or molecules that have gained or lost electrons, and therefore have a net positive or negative charge. Ions are formed when atoms or molecules lose or gain electrons in order to become more stable. For example, a sodium atom (Na) has 11 electrons. If it loses one electron, it becomes a sodium ion (Na+) with a +1 charge. A chlorine atom (Cl) has 17 electrons. If it gains one electron, it becomes a chloride ion (Cl) with a -1 charge.
Suspension in cell biology refers to the cultivation of cells in a liquid medium in which the cells are not attached to a surface. This is in contrast to adherent cell culture, in which cells are grown on a solid surface. It is a heterogeneous directive in which one or more component particle have particle size greater than 10-5 cm. very often particles are visible to the naked eye.
A true solution is a homogeneous mixture of two or more substances in which the particles of the solute are dissolved in the solvent at a molecular level. The solute particles are so small that they cannot be seen with the naked eye or even with a light microscope. True solutions are clear and transparent, and they do not scatter light. Example; sodium chloride in water forms a true solution and sugar or urea in water.
Colloids are heterogeneous mixtures of two or more substances in which the dispersed particles (called the colloid particles) are typically between 1 and 1000 nanometers in diameter. Colloids are not true solutions, because the colloid particles are large enough to scatter light, and they can eventually settle out of the solution given enough time. Example include; blood, cytoplasm, egg white etc.
THE PHYSICAL PROCESSES
The physical processes in the cell include the following;
Diffusion: Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. It is a passive process, meaning that it does not require energy. Diffusion is important for the movement of nutrients, gases, and other molecules into and out of the cell. Example; Oxygen and carbon dioxide diffusion between the lungs and the bloodstream, Nutrient diffusion between the digestive tract and the bloodstream, Waste product diffusion from the bloodstream to the kidneys ETC.
Osmosis: Osmosis is the movement of water across a semipermeable membrane. Semipermeable membranes allow some molecules to pass through, but not others. Osmosis is important for maintaining the water balance of the cell. Example, Water absorption by plant roots, Water reabsorption in the kidneys, Osmotic pressure in cells.
Plasmolysis is the shrinking of a plant cell due to the loss of water through osmosis. It occurs when the plant cell is placed in a hypertonic solution, which is a solution with a higher concentration of solutes than the cell cytoplasm. Water will move out of the cell through osmosis in order to equalize the concentration of solutes on both sides of the cell membrane. As the cell loses water, the cytoplasm will shrink away from the cell wall. Example, when a plant is wilted, when a plant is placed in a salty solution, when a plant cell is placed in a concentrated sugar solution.
Pinocytosis is the process by which cells take in substances from the outside world. In pinocytosis, the cell membrane folds in to form a small vesicle, which then pinches off and enters the cell. The vesicle contains extracellular fluid and the dissolved substances that were in it.
Phagocytosis is a process in which a cell covers a large particle, such as a bacterium or dead cell. The cell then digests the particle inside a specialized compartment called a phagosome. Phagocytosis is a key part of the immune system. It is how white blood cells called phagocytes remove bacteria, viruses, and other harmful invaders from the body. Phagocytes are also involved in clearing away dead cells and debris.
CELL DIVISION
Cell division happens when a parent cell divides into two or more cells called daughter cells. Cell division usually occurs as part of a larger cell cycle. All cells reproduce by splitting into two, where each parental cell gives rise to two daughter cells.
These newly formed daughter cells could themselves divide and grow, giving rise to a new cell population that is formed by the division and growth of a single parental cell and its descendant.
Types of Cell Division
There are two types of cell division: mitosis and meiosis. Most of the time when people refer to “cell division,” they mean mitosis, the process of making new body cells. Meiosis is the type of cell division that creates egg and sperm cells. The first one is vegetative division, wherein each daughter cell duplicates the parent cell called mitosis. The second one is meiosis, which divides into four haploid daughter cells.
Mitosis: The process in which cells use to make exact replicas of themselves. Mitosis is observed in almost all the body’s cells, including eyes, skin, hair, and muscle cells.
Meiosis: In this type of cell division, sperm or egg cells are produced instead of identical daughter cells as in mitosis.
Binary Fission: Single-celled organisms like bacteria replicate themselves for reproduction.
Phases of the Cell Cycle
There are two primary phases in the cell cycle:
Interphase: This phase was thought to represent the resting stage between subsequent cell divisions, but new research has shown that it is a very active phase.
M Phase (Mitosis phase): This is where the actual cell division occurs. There are two key steps in this phase, namely cytokinesis and karyokinesis.
The interphase further comprises three phases:
G0 Phase (Resting Phase): The cell neither divides nor prepares itself for the division.
G1 Phase (Gap 1): The cell is metabolically active and grows continuously during this phase.
S phase (Synthesis): The DNA replication or synthesis occurs during this stage.
G2 phase (Gap 2): Protein synthesis happens in this phase.
Quiescent Stage (G0): The cells that do not undergo further division exits the G1 phase and enters an inactive stage. This stage is known as the quiescent stage (G0) of the cell cycle.
There are four stages in the M Phase, namely:
Prophase
Metaphase
Anaphase
Telophase
MITOSIS
Mitosis is conventionally divided into 5 phases, which include prophase, prometaphase, metaphase, anaphase and telophase and cytokinesis. In interphase, a nuclear envelope surrounds the nucleus, the DNA is replicated in the S phase, and the sister chromatids join together at the central portion of the chromosome - the centromere. To organize the chromsome motion in the cell to help make division efficient as well as ensure all material is present in both daughter cells, the cell has centrosomes at each pole of the cell. Centrosomes organize the fibers of the mitotic spindle during mitosis that will help pull the sister chromatids apart.
In prophase, the chromatin fibers condense into chromosomes that are visible through a light microscope, each replicated chromosome appears as two identical sister chromatids joined at their centromeres, and the mitotic spindle begins to form. Also, the centrosomes begin to move to opposite poles of the cell, and they are propelled by the lengthening microtubules between them.
In prometaphase, the nuclear envelope falls apart; microtubules can now invade the nuclear area and bind to some of the chromosomes. The microtubules bind at the kinetochores, specialized protein structures at the centromere. Not all microtubules interact with kinetochores. Some microtubules interact with microtubules extending from the other side of the cell.
In metaphase, the centrosomes have migrated to opposite poles of the cell. The chromosomes have all lined up at the metaphase plate in the middle of the cell, and all chromosomes are attached to microtubules through their kinetochores. The metaphase plate is an imaginary line equidistant from the spindle’s 2 poles.
In anaphase, the shortest stage of mitosis, the sister chromatids break apart, and the chromosomes begin moving to opposite ends of the cell. By the end of anaphase, the 2 halves of the cell have an equivalent collection of chromosomes.
In telophase, 2 daughter nuclei form. The nuclear envelope beings to reappear. DNA begins to de-condense while spindle microtubules begin to depolymerize. Mitosis, the division of one nucleus into 2, is now complete. Lastly, cytokinesis, which is the division of the cytoplasm, takes place and the cell divides into 2 separate cells. In animal cells, this is accomplished through a cleavage furrow that pinches the cell in 2.
MEIOSIS
Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction. During reproduction, when the sperm and egg unite to form a single cell, the number of chromosomes is restored in the offspring.
Meiosis begins with a parent cell that is diploid, meaning it has two copies of each chromosome. The parent cell undergoes one round of DNA replication followed by two separate cycles of nuclear division. The process results in four daughter cells that are haploid, which means they contain half the number of chromosomes of the diploid parent cell.
Meiosis has both similarities to and differences from mitosis, which is a cell division process in which a parent cell produces two identical daughter cells. Meiosis begins following one round of DNA replication in cells in the male or female sex organs. The process is split into meiosis I and meiosis II, and both meiotic divisions have multiple phases. Meiosis I is a type of cell division unique to germ cells, while meiosis II is similar to mitosis.
Meiosis I, the first meiotic division, begins with prophase I. During prophase I, the complex of DNA and protein known as chromatin condenses to form chromosomes. The pairs of replicated chromosomes are known as sister chromatids, and they remain joined at a central point called the centromere. A large structure called the meiotic spindle also forms from long proteins called microtubules on each side, or pole, of the cell. Between prophase I and metaphase I, the pairs of homologous chromosome form tetrads. Within the tetrad, any pair of chromatid arms can overlap and fuse in a process called crossing-over or recombination. Recombination is a process that breaks, recombines and rejoins sections of DNA to produce new combinations of genes. In metaphase I, the homologous pairs of chromosomes align on either side of the equatorial plate. Then, in anaphase I, the spindle fibers contract and pull the homologous pairs, each with two chromatids, away from each other and toward each pole of the cell. During telophase I, the chromosomes are enclosed in nuclei. The cell now undergoes a process called cytokinesis that divides the cytoplasm of the original cell into two daughter cells. Each daughter cell is haploid and has only one set of chromosomes, or half the total number of chromosomes of the original cell.
Meiosis II is a mitotic division of each of the haploid cells produced in meiosis I. During prophase II, the chromosomes condense, and a new set of spindle fibers forms. The chromosomes begin moving toward the equator of the cell. During metaphase II, the centromeres of the paired chromatids align along the equatorial plate in both cells. Then in anaphase II, the chromosomes separate at the centromeres. The spindle fibers pull the separated chromosomes toward each pole of the cell. Finally, during telophase II, the chromosomes are enclosed in nuclear membranes. Cytokinesis follows, dividing the cytoplasm of the two cells. At the conclusion of meiosis, there are four haploid daughter cells that go on to develop into either sperm or egg cells.
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