Question

activity 21 - 1. physical factors in the environment
ecology is the branch of biology that deals with the relationship between living things and their environment. every organism is dependent upon its surroundings. among the physical factors in the environment that affect living organisms are soil, water, temperature, light, and nutrients.
soil
soil is a complex material that consists partly of organic matter and partly of inorganic matter (broken - down, or weathered, rock). the top layer of the soil, the topsoil, contains the decayed remains of plants and animals, which produce the black, rich, organic component of soil called humus. acids formed by the production of humus help to break down certain minerals in the soil. plant roots, various types of microorganisms, worms, insects, and larger, burrowing animals are found in the topsoil.
the three major types of soil are clayey soil, sandy soil, and loam. neither sandy or clayey soil contains much humus. clayey soil consists of very small particles that tend to pack tightly together. because of this tight packing, clayey soil does not contain much air, and water cannot pass through it readily. most plants do not grow very well in clayey soil. sandy soil consists of particles that are larger than that of clay. this type of soil is highly porous so that water passes through it very readily. sand does not hold enough water to support the growth of most plants. loam contains both clay and sand, but it also contains humus. it is porous enough to allow air and water to enter, but not so porous that they pass right through. most plants grow well in loam.
questions

1. what are the major components of soil?
2. the three main types of soils are _, _, and _.
3. most plants grow best in _.
4. what is humus, and how does it improve soil fertility?

water
the internal environments of living cells must be kept constant within certain narrow limits. this is accomplished in a variety of ways. in fish living in salt water, for example, there is a tendency for the cells to lose water by osmosis. to compensate for this loss, these fish drink large quantities of seawater. mineral ions in the seawater are absorbed from the

Explanation:

1. The text states that soil consists partly of organic matter and partly of inorganic matter (broken - down, weathered rock). The topsoil contains humus which is the decayed remains of plants and animals. So the major components are organic matter, inorganic matter, and humus in top - soil.
2. The text clearly mentions that the three major types of soil are clayey soil, sandy soil, and loam.
3. It is stated that most plants grow well in loam as it contains both clay and sand and also humus, and has the right porosity for air and water.
4. Humus is the decayed remains of plants and animals in the topsoil. The acids formed by humus production help break down certain minerals in the soil, thus improving soil fertility.

Answer:

1. Organic matter, inorganic matter, humus in top - soil
2. Clayey soil, sandy soil, loam
3. Loam
4. Humus is the decayed remains of plants and animals in the topsoil. Acids formed by its production help break down certain minerals in the soil, improving soil fertility.