Organisms and Their Environment: Quick Revision

A brief note on Organisms and Their Environment. Read it before a test. Try each question at the end before you open its answer.

The abiotic factors

• Four levels of ecology: organisms, populations, communities, biomes.
• Abiotic factors: temperature, water, light and soil. Biotic factors are the living parts.
• Temperature: below zero at the poles, above 50 °C in tropical deserts in summer, above 100 °C in thermal springs and deep sea vents. Eurythermal is a wide range, stenothermal a narrow range.
• Salinity (parts per thousand): inland waters below 5, the sea 30 to 35, hypersaline lagoons above 100. Euryhaline is a wide range, stenohaline a narrow range.
• Light: photoperiod, and the ultraviolet part is harmful. Soil: grains, pH and minerals decide the plants.

Responses and adaptations

• Regulate: birds and mammals keep a steady inside (homeostasis). Conform: most animals and nearly all plants.
• Migrate: the Siberian crane at Bharatpur. Suspend: hibernation (bear), aestivation (snail, fish), diapause (zooplankton), spores and seeds.
• Small animals lose heat fast, so they are rare in polar regions.
• Desert plant: Opuntia has spines, a flat stem for photosynthesis, a thick cuticle and stomata in pits. Kangaroo rat: water from fat, concentrated urine.
• Allen's rule: shorter ears and limbs in cold climates. Seal: blubber.
• High altitude: more red cells, less binding of oxygen by haemoglobin, faster breathing.

A worked example

A ball has a radius of 2 cm. What is its surface for each cm³ of volume?

1. The ratio is $3/r$.
2. $3 \div 2 = 1.5$ per cm.

Practice with new numbers

A program to try

The program names a sample of water from its salinity.

Mistakes to avoid

• Saying that abiotic means living. It means non-living.
• Mixing up eurythermal and stenothermal. Eury is wide and steno is narrow.
• Mixing up hibernation and aestivation. One is in winter and the other is in summer.
• Saying that the share of oxygen falls on a mountain. The pressure falls, and the share stays the same.

Check yourself

1. Which animals are the best regulators?

2. What is the salinity of the sea?

3. What does the kangaroo rat get water from?

4. What does Allen's rule say?

Sources

• NCERT (2023). Biology, Textbook for Class XII, chapter 11.
• Campbell Biology, 12th edition (2021), Pearson, chapters 40 and 52.
• OpenStax Biology 2e (2018), chapter 44, Ecology and the Biosphere.