Class 8 Geography Notes, Unit 1: Oceans and Seas -- Exercise Short/brief and Long/detailed Questions and Answers, for 8th Centralized Exam 2023 and onward, FDE, Islamabad

8th Class Geography Notes

Unit-1 

"Oceans and Seas"

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Class 8 Geography Unit-1 MCQs Preparation (Exercise)

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1. Exercise Short/Brief Questions and Answers:

Q1. What are the causes of Ocean Currents?

Ans:

Ocean currents are continuous, directed movements of ocean water caused by a number of factors. Ocean currents have specific names, directions, and speeds. Ocean Currents can be grouped into surface and deep currents. 

Surface Currents are caused by winds and their direction is modified by the effects of the rotation of the Earth and continental margins. Whereas deep currents are caused by salinity and temperature differences of the water.

Q2.  What are waves?

Ans:

Waves are a series of crests and troughs that are developed on the surface of the water by the dragging effects of the winds. Waves do not displace water from one place to another, rather they are the means of moving energy through water. Ripples, Chops, Swells, and Tsunamis are the types of waves.

Q3. How are Spring and Neap tides caused?

Ans:

On the basis of the relative positions of the Sun, Moon, and Earth there are two types of tides: -

Spring Tides: When the Sun, Moon, and Earth are in a straight line, high tides rise to higher levels and low tides fall to a lower level than normal. These higher high tides and lower low tides are called spring tides and they occur on the occasions of Full and New Moon.

Neap Tides: When the Sun and Moon are at right angles with respect to the Earth, high tides do not rise so high, and low tides do not fall so low. Such moderate tides are known as neap tides and they occur on the 7th and 21st days of the Moon.

Q4.  Differentiate between Isthmus from Strait.

Ans:

Isthmus	Strait
Definition: An isthmus is a narrow strip of land connecting two land masses and separating two water bodies.	Definition: A strait is a narrow passage of water bodies connecting two large water bodies.
Example1: The Isthmus of Panama is a narrow strip of land between the Caribbean Sea and the Pacific Ocean. It links South and north America.	Example1: Gibraltar Strait connects the Mediterranean Sea and the Atlantic Ocean.
Example2: The Isthmus of Suez is a narrow strip of land between the Red Sea and the Mediterranean Sea connecting the continents of Asia and Africa.	Example2: Malacca Strait is located between Malaysia and Indonesia. It links the Indian Ocean and the South China Sea.

Q5. Write the names of the five major seas of the world?

Ans:

Major seas of the world:

Following are the names of the major seas of the world:-

1. Mediterranean seas

2. Caribbean seas

3. Black seas

4. Arabian seas

5. Caspian sea

2. Long/Detailed Questions and Answers:

Q1. Describe the main characteristics of major oceans?

Ans:

Major Oceans of the World:

There are five major oceans on Earth. According to the location, size, and average depth, each ocean has its own distinct characteristics:

1. Pacific Ocean: 

The Pacific Ocean is the largest and deepest ocean of the world, covering an area of 165 million square kilometers. It is bordered by North and South America, Asia, Australia, and the Southern Ocean (Antarctic Ocean). Its average depth is approximately 4000 meters, Its deepest part is located near the Mariana Islands, which is named Mariana Trench. Mariana Trench is about 10,924 meters deep. Thousands of islands of different sizes are located in the Pacific Ocean.

2. Atlantic Ocean: 

The Atlantic Ocean is the second-largest ocean of the world. It covers an area of about 106 million square kilometers. It is bounded by Europe and Africa in the East and by North and South America in the West. In the South, it is bordered by the Southern Ocean. Its average depth is 3646 meters. Its deepest point is Puerto Rico Trench which is 8600 meters deep.

3. Indian Ocean: 

It is the third-largest ocean on the world. It covers an area of about 70 million square kilometers. It is situated between Africa, Asia, Australia, and the Southern Ocean. Its average depth is 3750 meters, and its deepest point is Java Trench (7258 meters). It is located about 300 km off the coast of Sumatra, Indonesia.

4. Antarctic/ Southern Ocean: 

The Southern Ocean is the fourth largest ocean of the world. It occupies an area between 60 degrees southern latitude and the coast of Antarctica. Its total surface area of 120 million square kilometers its average depth is 3270 meters and its deepest point (South Sandwich Trench) is about 7235 meters deep.

5. Arctic Ocean: 

The Arctic Ocean is the smallest and shallowest of the world's oceans, covering an area of 14 million square meters. It is situated around the North Pole and is bounded by Europe, Asia, and North America. It has an average depth of 1000 meters and its deepest point is named Fram Basin, which is 5645 meters deep.

Q2. Explain the role of Marine biodiversity in our environment?

Ans:

Role of Marine Biodiversity in our Environment: 

Marine biodiversity plays a very important role in shaping and maintaining our physical environment in the following ways:-

(i). Marine plants supply about 50% of the oxygen to the atmosphere. About 26% of the carbon dioxide emitted through human activities is absorbed by them

(ii). The amount of energy produced per unit area by plants in one year is called primary productivity. Half of the world's Net Primary Productivity comes from marine plants. These plants serve as the basic food for all types of oceanic life. Smaller marine animals that consume these plants become a source of food for larger marine animals.

(iii). Fishing provides high-quality protein fish and fishery products provide food security to hundreds of millions of people.

(iv). Marine plants such as kelp and seagrass, together with reefs provide habitats for many marine life forms, such as shrimp, fish, and molluscs.

(v). Gastropods (marine snails and slugs) and shrimps that feed on microalgae eventually become food for larger crabs, lobsters, and fish.

Q3. What are the possible threats to the ocean?

Ans:-

Possible Threats to the Ocean:

Only 13% of the total area covered by oceans remains untouched by the damaging impacts of human activities. Most of the oceans are under the Influence of human activities. Some such activities are:

Oil & Gas Drilling: 

Offshore drilling results in the spilling of crude oil, natural gas liquids, diesel, or hydraulic fluid into surrounding marine environments. These chemicals kill or damage plankton, coral reefs, small fish, and larvae.

Pollution: 

Pollution is a huge problem faced by marine ecosystems as large quantities of garbage and waste are continuously being dumped into oceans.

Over-fishing: 

Humans are catching more and more fish every year, leading to serious marine biodiversity losses.

Ocean Acidification: 

Industrial activities have been emitting large amounts of carbon dioxide Into the Earth's atmosphere. A significant portion of this carbon dioxide is absorbed by seawater resulting in an increased concentration of hydrogen ions. This makes the seawater more acidic.

Mangrove Deforestation: 

Mangrove forests act as buffer zones between land and sea, they protect coastal land from erosion and serve as breeding and nursery grounds for a variety of marine life forms such as fish, amphibians, reptiles, birds, and mammals. Cutting down mangroves causes harmful impacts on marine ecosystems.

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