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

The levels of organization from cells to organ systems are as follows:
1. Cell
2. Tissue
3. Organ
4. Organ system

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.

The smooth muscle in the stomach is primarily responsible for:
i. Churning and mixing food with stomach acid.
ii. Producing chyme by contracting and relaxing in a coordinated manner which helps with digestion and propels the partially digested food into the small intestine through a process called peristalsis.
iii. It facilitates the movement and mechanical breakdown of food within the stomach.

Palisade mesophyll in a leaf is responsible for photosynthesis. It consists of tightly packed elongated cells with large number of chloroplasts to absorb light and produce food for plants.

The shoot system consists of two portions: the vegetative (non-reproductive) parts of the plant, such as the leaves and the stems, and the reproductive parts of the plant, which include flowers and fruits. The shoot system generally grows above ground, where it absorbs the light needed for photosynthesis.

Homeostasis is defined as the body's ability to maintain a stable internal environment despite the changes in the external environment.

Importance Homeostasis is important for organisms because it regulates the body temperature, blood pressure, blood sugar and pH levels.

First, high temperature will be detected by sensors-primarily nerve cells with endings in your skin and brain and relayed to a temperature-regulatory control centre in your brain. The control centre will process the information and activate effectors such as the sweat glands whose job is to oppose the stimulus by bringing body temperature down.

i) Tissue and organ

Tissue In multicellular organism, cells make tissue. A tissue is a group of similar cells that work together to perform one or more specific functions. Example: Muscle tissue, epithelial tissue.

Organ An organ is a structure made up of related tissues working together to perform specific function. Example: Stomach, heart and kidney.

ii) Root system and shoot system

Root System

• The root system consists of two main structures including the root cap and the primary root.
• The root system anchors the plant and absorbs water and nutrients.

Shoot System

• The shoot system consists of two portions: the vegetative and reproductive parts of the plant.
• The shoot system components stems, leaves and reproductive structures like flowers work together to enable processes like photosynthesis and reproduction.

iii) Epidermal and mesophyll tissue

Epidermal tissue

• The outermost layer of leaf is made of epidermal tissue (epidermis).
• The upper epidermis is usually covered by waxy cuticle, which reduce 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.

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: Palisade mesophyll and Spongy mesophyll.

iv) Palisade and spongy mesophyll

Palisade Mesophyll

• It is located just beneath the upper epidermis.
• It consists of tightly packed elongated cells.
• Their cells are rich with chloroplasts and has major role in photosynthesis

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.

(i) Stomach is an organ specialized for the digestion of proteins and storing food.

(ii) Stomach has:
(a) Epithelial (glandular) tissues which secrete the gastric juice.
(b) Muscular tissues which perform contractions of stomach walls for grinding of food, mixing enzyme with food and moving food to posterior end.

Level of organization | Examples
Atomic level | Zinc, nitrogen
Molecular level | Carbon dioxide, protein
Organelle level | Cilia
Cellular level | Neuron, Guard cell
Tissue level | Xylem, epidermis
Organ level | Brain, leaf
Organ system level | Root system
Organism level | Rose plant, cat

In higher multicellular organisms, particularly in animals, different organs performing related functions are organized together in the form of an organ system. For example, digestive system carries out process of digestion. It consists of oral cavity, stomach, small intestine, large intestine, liver and pancreas.

An enormous number of biomolecules become associated in a particular way and form organelles. The organelles are actually sub-cellular structures, e.g. mitochondria, ribosomes etc.

A group of similar or different types of cells performing same function e.g. xylem and phloem in plants, are composed of different cells while nervous tissues are composed of same type of cells.

A cell works as an open system i.e. it takes in substances needed for its metabolic activities through its cell membrane. It takes up food, oxygen, water and salts for survival, growth and division, and energy for metabolic processes. Products and by-products are formed in metabolism. Cell either utilizes the products or transport them to other cells. The by-products are either stored or are excreted out of cell.

The structure of epithelial tissue matches with its function in different parts of body. As in the skin it provides protection as it has multiple layers to protect against injury and germs. In the lungs it plays role in diffusion and filtration by allowing oxygen and carbon dioxide exchange. It also plays role in secretions (found in sweat glands, salivary glands, and the stomach) and absorption in the intestines, it has tiny folds to absorb nutrients efficiently.

Organ systems need to collaborate to maintain proper body functioning. While each system has its own role, they are all interconnected. For example, the circulatory system supplies oxygen from the respiratory system to brain and all body cells. If the circulatory system fails, the other systems (e.g., respiratory and muscular) cannot get oxygen and nutrients, leading to malfunction and affecting the entire body.