Unit 5: Tissues, Organs and Organ Systems — Long Questions

Introduction
Organisms are built on a pattern of increasing complexity. The levels of organization in multicellular organisms begin with the smallest unit, the atom, and progress to the most complex level, the organism.

Level of Organization

1. Atom
Definition
Atoms are the smallest unit of matter that maintain the property of an element.
Examples
Carbon, Hydrogen and Oxygen etc.

2. Molecule
Definition
Atoms combine to form molecules which can have entirely different properties than the atoms they contain.
Examples
Water, protein and nucleic acid etc.

3. Organelle
Definition
Molecules combine in specific ways and make the subcellular level i.e., organelle. Each organelle is specialized to do a particular function.
Examples
Mitochondria are responsible for cellular respiration and ribosomes are specialized for protein synthesis.

4. Cell
Definition
When organelles assemble and interact with each other, they make cell - the smallest unit with characteristics of life. They can carry out life activities and can also reproduce.
Examples
Unicellular organisms are made of only one cell while multicellular organisms are made of many cells.

5. Tissue / What is a tissue level? Explain plant and animal tissues.
Introduction
In multicellular organisms, cells make tissues. A tissue is a group of similar cells that work together to perform one or more specific functions.

Examples
In animals

• Epithelial tissue - covers body surfaces and lines cavities (e.g., skin)
• Muscle tissue - enables movement (e.g., cardiac muscle in the heart) In plants
• Epidermal tissue - protects the underlying parts (e.g., epidermis of leaf)
• Vascular tissue - transports water and nutrients (e.g., xylem and phloem)

6. Organ
Definition
An organ is a structure made up of related tissues working together to perform specific functions.
Examples

• In animals: Heart (pumps blood through the circulatory system), and lungs (facilitate gas exchange).
• In plant: Leaves (conduct photosynthesis), and roots (absorb water and nutrients from soil).

7. Organ System
Introduction
An organ system consists of multiple organs that work together to perform related functions.
Examples

• In animals - circulatory system (transports nutrients and oxygen throughout the body) and digestive system (breaks down food and absorbs nutrients).
• In plants - root system (anchors the plant and absorbs water and nutrients) and shoot system (supports the plant and conducts photosynthesis).

8- Organism
Introduction
An organism is a living entity that can function independently on behalf of proper functioning of its organ systems whose functions are coordinated to one another.
Examples
Examples include humans and trees.

Introduction
In organisms, the components at each level do not work solely. Instead, they interact with each other. Due to their interactions, they create new functions called emergent properties. These include the abilities that are present in higher level or organization but are not possible from the individual components.

Examples
Following are the examples of emergent properties when lower levels make higher levels:

1- From Organelles to Cells: Individual organelles have specific functions. However, when these organelles interact within a cell, they create a complex system capable of carrying out various cellular processes, such as metabolism, protein synthesis, and energy production.

2- From Cells to Tissues: Individual cells do not have properties that are present in the tissue which they make. For example, muscle cells combine to form muscle tissue, which can contract and generate force.

3- From Tissues to Organs: An organ performs complex functions that its individual tissues cannot perform. For example, the heart is composed of various tissues, including muscle tissue, connective tissue, and epithelial tissue. The coordinated interaction of these tissues allows the heart to pump blood throughout the body.

4- From Organs to Organ Systems: Multiple organs working together form organ systems, which carry out vital functions. For example, the digestive system is composed of organs like the mouth, oesophagus, stomach, intestines, and liver. These individual organs cannot digest food but the coordinated actions of these organs enable the digestion and absorption of nutrients.

5- From Organ Systems to Organisms: In an individual, the interactions of various organ systems bring emergent properties such as consciousness, thinking, and the ability to adapt to environment. These complex behaviours are not present in individual organ system but arise from their coordinated interactions.

Introduction
Organs are made of two or more types of tissues organized to serve a particular function. Organs which perform related functions work together and make an organ system. The following are examples of organs and organ system in plants.

Organs in Plants

Roots Roots are usually found underground; anchor the plant in the soil and absorb water and essential minerals from the soil. Roots also store nutrients that the plants use for their growth.

Stems Stems are above-ground structures that support leaves, flowers, and fruits. Stems contain vascular tissues (xylem and phloem) that facilitate the movement of water, minerals, and nutrients between roots and leaves.

Leaves Leaves are the primary sites of photosynthesis and transpiration (loss of water vapour through small pores called stomata in leaves).

Flower Flower is reproductive part of a plant. It plays a crucial role in plant's sexual reproduction.

Leaf as an Organ

(a) Introduction
In plants, leaf is a complex organ made of various related tissues.

(b) Major tissues of a leaf / Describe the tissue composition of the leaf. how does each tissue contribute to the functioning of the leaf?

The major tissues that form a leaf are:

1- Epidermal Tissue: The outermost layer of leaf is made of epidermal tissue (epidermis). The upper epidermis is usually covered by waxy cuticle, which reduces water loss and provides protection. The lower epidermis often contains guard cells. Two guard cells enclose a stoma (plural stomata), which are tiny pores that regulate gas exchange and water vapour loss.

2- Mesophyll Tissue: This tissue lies between the upper and lower epidermis. It consists of cells rich in chloroplasts. It is the site of photosynthesis. It is divided into two distinct regions.
i. Palisade Mesophyll: It is located just beneath the upper epidermis. It consists of tightly packed elongated cells.
ii. Spongy Mesophyll: It is present below the palisade mesophyll. It is composed of loosely arranged cells with air spaces between them. These air spaces facilitate the diffusion of gases throughout the leaf.

3- Vascular Tissue: It arranged in the midrib and veins in leaf. It is categorized as complex tissue because it consists of two tissues i.e., xylem and phloem.
i. Xylem
The xylem of leaf conducts water and dissolved minerals from the xylem of stem to leaf cells.
ii. Phloem
Phloem tissue transports the products of photosynthesis (sugars) from leaf cells to the phloem of stem.

Organ Systems in Plants

a) Introduction
In plants, the organ system level is less complex than in animals. However, plants do exhibit some level of organization in terms of tissues and structures that work together for specific functions.

b) Examples
The root system anchors the plant and absorbs water and nutrients, while the shoot system includes stems, leaves, and reproductive structures like flowers. These components work together to enable processes like photosynthesis and reproduction.

Organs in Human Body
Various organs are present in human body, each with specific functions. Here are a few of the most important organs.

Heart The heart is a muscular organ that pumps blood throughout the body. It is essential for delivering oxygen and nutrients to cells and removing waste products.

Lungs The lungs are responsible for breathing, allowing the exchange of oxygen and carbon dioxide between the body and the environment.

Brain The brain is the control center of the body, responsible for thoughts, emotions, and movements.

Liver The liver performs many vital functions, including filtering blood, producing bile, and storing glucose.

Kidneys The kidneys are responsible for filtering waste products from the blood and producing urine.

Stomach The stomach is a muscular organ that breaks down food using digestive enzymes.

Intestines The intestines are long, tubular organs that absorb nutrients from food.

Pancreas The pancreas produces digestive enzymes and hormones, such as insulin and glucagon.

Stomach as an Organ / Describe the tissues composition of the stomach. How does each tissue contribute to the digestive function of the stomach?

Stomach is responsible for the breakdown of proteins through mechanical and chemical processes and for storing food. It is composed of the following tissues that contribute to its functions:

1- Epithelial Tissue: The inner wall is made up of epithelial tissue. It is glandular in nature and secretes mucus. The mucus lines the inner wall and protects it from acids. This tissue also secretes gastric juice that contains enzyme pepsinogen for protein digestion and hydrochloric acid for activating pepsinogen to pepsin enzyme and to kill germs.

2- Connective Tissue: It lies beneath epithelial tissue. It provides structural support and contains blood vessels, nerves, and lymphatics.

3- Muscle Tissue: There are three layers of smooth muscles; the outer longitudinal layer, the middle circular layer, and the inner oblique layer. These muscle churn and mix the food in stomach.

4- Outer Connective Tissue: It is the outermost layer that encircles the stomach and supports it

Organ Systems in Human Body / How do the organ systems come together to form the human body?

Following are a few examples of organ systems which form the human body.

1. Skeletal System
Parts
It consists of bones, cartilages and tendons.
Functions
It provides structure, support, and protection for the body. It serves as a framework for muscles to attach, allowing movements. It also stores minerals and produces blood cells.

2. Digestive System
Parts
It consists of organs such as mouth, oesophagus, stomach, small intestine, and large intestine.

Functions
This system is responsible for the break down and absorption of nutrients from food.

3. Respiratory System
Parts
It includes the lungs, trachea (windpipe), and bronchi (air tubes).
Functions
This system is involved in the exchange of gases (oxygen and carbon dioxide) between the body and the environment.

4. Muscular System
Parts
It includes skeletal muscles, which attach to bones and contract to produce movements.
Functions
This system allows movement and provides structural support for the body.

5. Nervous System
Parts
It includes brain, spinal cord, and nerves.
Functions
The nervous system coordinates and controls body functions through nerve impulses.

6. Blood Circulatory System
Parts
It includes heart, blood vessels (arteries, veins, and capillaries), and blood.
Functions
This system transports oxygen, nutrients, hormones, and waste products throughout the body.

Introduction
The organs and organ systems of the body work in coordination to maintain a stable internal environment. It is called homeostasis. Homeostasis is defined as the body's ability to maintain a stable internal environment despite the changes in the external environment.

Examples
Examples of homeostasis include regulating the temperature, blood pressure, blood sugar, and pH levels.

Importance of Homeostasis

Homeostasis plays a vital role in supporting overall health and well-being. For example;

• Each cell is a sophisticated machine that plays a precise role within the body. The functioning of cell is possible only when extracellular conditions such as temperature, pH and concentrations of salts, the glucose and oxygen are kept in normal range.

• When we do hard work, our muscles produce heat that raises the body temperature. In such situation, the temperature regulating centre (hypothalamus) in the brain sends message to sweat glands. As a result, sweating occurs to cool down the body.

• When the body temperature falls, the temperature regulatory centre sends message to muscles. As a result, shivering occurs to generate heat.

• When we drink juice, blood glucose level rises. Special glands (pancreas) in the body release a hormone insulin in blood. This hormone lowers the blood glucose level to normal.

• When we do hard exercise, our muscles need more oxygen. In such condition, the rate of respiration and heartbeat are increased. Accelerated respiration and heartbeat supply more oxygen and food to the muscles for continuous work.

Role of Organ Systems in Homeostasis

(a) Introduction
Several organ systems work together to maintain homeostasis.

(b) Examples

1. Nervous system and Endocrine system
Nervous system and endocrine system regulate and coordinate activities such as heart rate, respiration, metabolism, and response to stress.

2. Respiratory System
Respiratory system ensures that the body receives enough oxygen for cellular respiration. It also expels excess carbon dioxide from the body.

3. Cardiovascular System
Cardiovascular system regulates body temperature and pH levels. It also ensures that all cells receive the necessary substances for proper function.

4. Digestive System
Digestive system works for proper distribution of nutrients to cells for energy, growth, and repair.

5. Muscular and Skeletal Systems
Muscular and skeletal systems help and maintain body posture, support and movement.

Structure of Plant Root System

The root system consists of two main structures including the root cap and the primary root. The primary root is characterized by the root meristem, the meristematic region, the region of elongation and the maturation region. Lateral roots grow from the primary root.

Functions of Plant Root System

This system has three major jobs:
i. Absorbing water and minerals
ii. Anchoring and supporting the plant
iii. Serves as a storage site for food.

Working of Organ system

The respiratory system and the circulatory system work closely together to deliver oxygen to cells and get rid of the carbon dioxide that these cells produce. The circulatory system picks up oxygen in the lungs and drops it off in the tissues, then performs the reverse function for carbon dioxide. The lungs expel the carbon dioxide and bring in new oxygen containing air. Only when both systems are working together can oxygen and carbon dioxide be successfully exchanged between cells and environment.

• Digestive system works for proper distribution of nutrients to cells for energy, growth, and repair.

• Urinary system eliminates waste products form the body. It also maintains blood volume, blood pressure, and pH levels.