Free Biology Tutorial on Living Organisms [Well Explained]

This Biology Tutorial will focus on LIVING ORGANISMS. This topic has been explained to ensure you understand it very well. At the end of the tutorial, you can download it for FREE. Please share this page with your friends who may need it.

Allow us to use this medium to explain everything you need to know about the living organisms.

We’ll tell you the characteristics of living organisms.

That’s not all.

We’ll also show you the cell structure and functions of cell components.

Then we will tell you the level of organization for cell, tissue, organ, systems, and organisms.

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We will round up the tutorial with practice questions to ascertain your level of understanding on living organisms.

It’s our pleasure to take you on this tutorial. Let’s not waste another second.

Page Contents

Living Organisms and their Characteristics
Cell Structure and Functions of Cell Components
Level of Organization
Practice Questions
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Living Organisms and their Characteristics

Living organisms are entities that exhibit life processes, characteristics, and functions. These entities are distinguished from non-living matter by their ability to carry out certain essential activities that are indicative of life.

While there are exceptions and debates on the boundaries of life, common characteristics of living organisms include:

Cellular Structure: Living organisms are composed of one or more cells, which are the basic units of life. Cells carry out various functions and activities necessary for the organism’s survival.
Metabolism: Living organisms engage in metabolic processes, which involve the conversion of nutrients into energy and the synthesis of molecules essential for growth, repair, and reproduction.
Homeostasis: Living organisms maintain a stable internal environment despite external changes. This balance is crucial for optimal functioning and survival.
Growth and Development: Living organisms undergo growth, increasing in size or complexity over time. Development refers to changes in the structure and function of an organism throughout its life cycle.
Reproduction: Living organisms can produce offspring, either sexually or asexually, ensuring the continuation of their species.
Response to Stimuli: Living organisms can respond to external stimuli from their environment. This responsiveness allows them to adapt to changing conditions and interact with their surroundings.
Adaptation and Evolution: Living organisms have the capacity to adapt to their environment over generations. Through the process of evolution, populations of organisms can undergo changes in their genetic makeup over time.
Complex Organization: Living organisms exhibit a high degree of complexity and organization in their structure, from molecules to cells, tissues, organs, and organ systems.

Didn’t get any of the above???

Now imagine living organisms as a big group of really cool characters, each with its own special powers and things it can do. Here are some key things that make these characters special:

Tiny Builders (Cells): Just like a superhero team has members, living organisms have tiny builders called cells. These cells are like the superheroes that work together to make everything happen.
Super Fuel (Metabolism): Living organisms need to eat, just like you do. But what’s even cooler is that they turn their food into super fuel that gives them energy to grow and do all sorts of amazing things.
Clean Freaks (Homeostasis): Imagine if superheroes had a special power to keep their headquarters super clean and just right. Living organisms have a similar power—they can keep their insides just the way they like it to stay healthy.
Growth Spurts (Growth and Development): Think about how you grow taller and smarter each year. Living organisms do the same thing. They start small, and as time goes on, they get bigger and learn new things.
Family Builders (Reproduction): Living organisms can have families too! They can make more of themselves, like when a superhero has sidekicks to join the adventure.
Super Sensors (Response to Stimuli): Living organisms are like superheroes with super senses. They can feel things around them and react, kind of like how you put on a sweater when you’re cold.
Adapting Experts (Adaptation and Evolution): Imagine if superheroes could change their costumes to be better at fighting villains. Living organisms can change a little bit over a really long time to become better at living in their homes.
Team Players (Complex Organization): Living organisms are like a big team, where every player has a special job. From the tiniest parts to the biggest parts, everything works together like a super squad.

So, living organisms are basically a fantastic group of characters, each with its own unique abilities, working together to have an awesome adventure called life!

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Cell Structure and Functions of Cell Components

Cell structure refers to the organization and components of a cell, which is the basic structural and functional unit of living organisms. Cells vary in structure based on their type (e.g., prokaryotic or eukaryotic) and function, but there are common features shared by most cells.

Here is a brief overview of cell structure:

Cell Membrane: The cell membrane, or plasma membrane, surrounds the cell and separates its internal environment from the external surroundings. It controls the passage of substances in and out of the cell.
Cytoplasm: The cytoplasm is the gel-like substance that fills the cell and surrounds the cellular organelles. It provides a medium for cellular activities and contains various molecules and structures.
Nucleus: In eukaryotic cells, the nucleus is a membrane-bound organelle that houses the cell’s genetic material, DNA. It serves as the control center for cellular activities and is involved in the regulation of gene expression.
Organelles: Organelles are specialized structures within the cell that perform specific functions. Examples include the endoplasmic reticulum, Golgi apparatus, mitochondria, chloroplasts (in plant cells), lysosomes, and more.
Endoplasmic Reticulum (ER): The endoplasmic reticulum is a network of membranes involved in the synthesis and transport of proteins and lipids. Rough ER has ribosomes on its surface, while smooth ER lacks ribosomes.
Golgi Apparatus: The Golgi apparatus processes, modifies, and packages proteins and lipids produced by the endoplasmic reticulum. It plays a key role in the secretion of these products.
Mitochondria: Mitochondria are the powerhouse of the cell, responsible for generating energy in the form of ATP through cellular respiration. They have their own DNA and are believed to have originated from an ancient symbiotic relationship.
Cytoskeleton: The cytoskeleton is a network of protein filaments (microfilaments, microtubules, and intermediate filaments) that provides structural support to the cell, maintains its shape, and is involved in cellular movements.
Centrioles: Centrioles are involved in the organization of microtubules during cell division, specifically in the formation of the mitotic spindle in animal cells.
Vacuoles and Vesicles: Vacuoles are membrane-bound sacs that store substances within the cell. In plant cells, large central vacuoles store water and nutrients. Vesicles are smaller membranous sacs involved in transport within the cell.

Are those explanations difficult for you to understand?

Now let’s try make it very easy for you.

Think of a cell as a tiny city with lots of different parts, each doing a special job to keep the city running smoothly.

City Wall (Cell Membrane):
- Function: Like the city wall, the cell membrane protects the cell. It decides what comes in and out, just like a gatekeeper.
Control Center (Nucleus):
- Function: The nucleus is like the city’s control center. It holds the cell’s instructions (DNA) for how to do everything. It’s like a tiny city planner.
Power Plants (Mitochondria):
- Function: These are like power plants providing energy for the city. They turn food into energy that the cell can use, just like a power station.
Factories (Endoplasmic Reticulum and Golgi Apparatus):
- Function: These parts are like factories. They make and package things the cell needs, such as proteins and other important molecules.
Garbage Collectors (Lysosomes):
- Function: Lysosomes are like garbage collectors. They clean up waste and recycle old parts, keeping the city clean.
Transportation System (Cytoplasm):
- Function: The cytoplasm is like the roads in the city. It helps things move around inside the cell, so everything gets to where it needs to go.

Teamwork in Action: Imagine the cells are like a team of workers in this tiny city. Each worker (cell component) has a specific job, and when they all do their jobs well, the city (cell) stays healthy and happy.

So, cells are the building blocks of living things, and just like in a city, each part plays a crucial role in keeping everything working smoothly!

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Level of Organization

The levels of biological organization span from the smallest unit of life, the cell, to the highest level, the organism.

Each level builds upon the previous one, contributing to the overall structure and function of living entities.

i. Cell:

Examples: Euglena and Paramecium
Explanation: Cells are the basic structural and functional units of living organisms. Euglena and Paramecium are both single-celled organisms belonging to the protist kingdom. They exhibit characteristics of living cells, including a cell membrane, cytoplasm, and organelles.

ii. Tissue:

Examples: Epithelial tissues in animals and Hydra (a simple multicellular organism)
Explanation: Tissues are groups of cells working together to perform specific functions. In animals, epithelial tissues form coverings and linings. Hydra is a simple multicellular organism that also has tissues, although it is less complex than higher organisms.

iii. Organ:

Example: Onion bulb
Explanation: Organs are composed of different tissues working together to perform specific functions. The onion bulb is an organ that consists of various tissues, including epidermal tissues, storage tissues, and vascular tissues.

iv. System:

Examples: Reproductive system, digestive system, excretory system
Explanation: Systems are groups of organs working together to carry out a particular function. For example, the reproductive system includes organs like the testes or ovaries, the digestive system includes the stomach and intestines, and the excretory system involves organs like the kidneys.

v. Organism:

Example: Chlamydomonas
Explanation: An organism is an individual living being. Chlamydomonas is a single-celled green alga, representing the entire living entity. It is a complete and independent unit capable of carrying out all life processes at the cellular level.

That’s all we’ll cover in this tutorial.

We have been able to explain living organisms and their characteristics, cell structures and functions of cell components, and the level of organization.

Now test your level of understanding by answering these practice questions.

Practice Questions

1. Which characteristic of living organisms involves the maintenance of a stable internal environment despite external changes?

A) Metabolism
B) Homeostasis
C) Reproduction
D) Adaptation

2. What is the primary function of the rough endoplasmic reticulum in a cell?

A) ATP production
B) Lipid synthesis
C) Protein synthesis
D) Carbohydrate storage

3. Which organelle is responsible for breaking down cellular waste and old organelles?

A) Nucleus
B) Lysosome
C) Golgi apparatus
D) Mitochondria

4. In which level of biological organization do tissues and organs work together to perform specific functions?

A) Cellular
B) Tissue
C) Organ
D) System

5: What is the significance of DNA in living organisms?
A) It produces energy
B) It regulates gene expression
C) It forms the cell membrane
D) It synthesizes proteins

6. Which cellular structure is responsible for maintaining cell shape and facilitating cellular movements?

A) Nucleus
B) Endoplasmic reticulum
C) Cytoskeleton
D) Golgi apparatus

7. What is the function of chloroplasts in plant cells?

A) Cellular respiration
B) Photosynthesis
C) Protein synthesis
D) Lipid storage

8: At which level of organization do organisms evolve over time through natural selection?

A) Cellular
B) Tissue
C) Organ
D) Population

9. Which characteristic distinguishes living organisms from non-living matter based on their ability to produce offspring?

A) Growth
B) Reproduction
C) Homeostasis
D) Metabolism

10. In eukaryotic cells, which organelle is involved in the synthesis and modification of proteins?

A) Nucleus
B) Golgi apparatus
C) Mitochondria
D) Lysosome

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Answers and Explanations

Answer: B) Homeostasis
- Explanation: Homeostasis is the characteristic of living organisms that involves the maintenance of a stable internal environment despite external changes.
Answer: C) Protein synthesis
- Explanation: The rough endoplasmic reticulum is studded with ribosomes and is involved in the synthesis and modification of proteins.
Answer: B) Lysosome
- Explanation: Lysosomes are membrane-bound organelles containing enzymes that break down cellular waste and old organelles.
Answer: C) Organ
- Explanation: Tissues and organs work together at the organ level to perform specific functions within an organism.
Answer: B) It regulates gene expression
- Explanation: DNA in living organisms carries genetic information and regulates the expression of genes, influencing the synthesis of proteins and other molecules.
Answer: C) Cytoskeleton
- Explanation: The cytoskeleton, made up of protein filaments, provides structural support to the cell and is involved in cellular movements.
Answer: B) Photosynthesis
- Explanation: Chloroplasts in plant cells are responsible for photosynthesis, the process by which plants convert light energy into chemical energy.
Answer: D) Population
- Explanation: Evolution occurs at the population level, where the frequency of traits in a group of organisms changes over successive generations.
Answer: B) Reproduction
- Explanation: Reproduction is the characteristic that involves the production of offspring, ensuring the continuation of a species.
Answer: B) Golgi apparatus
- Explanation: The Golgi apparatus is involved in the synthesis, modification, and packaging of proteins and lipids produced by the endoplasmic reticulum.