Characteristics of living organisms Revision Notes

Movement in living organisms involves a change in position or location of the whole organism or parts of it. This can be voluntary, such as animals walking or swimming, or involuntary, such as the opening and closing of plant leaves or the movement of cilia in single-celled organisms.

For example, a cat moves by walking to catch prey, while a sunflower turns its head towards the sun, demonstrating movement of parts rather than the entire organism.

Movement is essential for finding food, escaping predators, and responding to environmental changes.

• Whole-organism movement: animals walking, swimming, flying.
• Movement of parts: plant leaves orienting to light, amoeba extending pseudopodia.
• Movement enables interaction with the environment and survival.

Respiration is the set of chemical reactions in cells that break down nutrient molecules, such as glucose, to release energy. This energy is vital for all metabolic activities, including growth, movement, and repair.

The general equation for aerobic respiration is: glucose + oxygen → carbon dioxide + water + energy (ATP).

For example, human cells respire glucose to produce energy for muscle contraction during exercise. Yeast cells respire anaerobically in the absence of oxygen, producing energy and ethanol as a by-product.

• Aerobic respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy.
• Energy released powers cellular processes.
• Anaerobic respiration occurs in some organisms when oxygen is scarce.

Sensitivity is the ability of an organism to detect changes in its internal or external environment and respond appropriately. This allows organisms to maintain homeostasis and adapt to their surroundings.

For example, plants bend towards light (phototropism), and humans withdraw their hand quickly from a hot surface (reflex action).

Sensitivity involves receptors that detect stimuli and effectors that produce responses.

• Stimulus detection by receptors (e.g., light, temperature, chemicals).
• Response by effectors (muscles, glands, growth changes).
• Maintains internal balance and environmental adaptation.

Growth in living organisms is a lasting increase in size and dry mass due to cell division and enlargement. It is a key indicator of life and development.

For example, a seedling grows taller and develops more leaves over time, increasing its biomass.

Growth requires energy and raw materials obtained through nutrition and is regulated by genetic and environmental factors.

• Cell division and enlargement cause growth.
• Measured as increase in size and dry mass.
• Dependent on nutrition and energy supply.

Reproduction is the biological process by which organisms produce offspring of the same species, ensuring survival of the species.

It can be sexual, involving the fusion of gametes (e.g., humans, flowering plants), or asexual, where offspring arise from a single parent (e.g., bacteria by binary fission).

Reproduction maintains genetic continuity and allows adaptation through genetic variation in sexual reproduction.

• Sexual reproduction involves gametes and genetic variation.
• Asexual reproduction produces genetically identical offspring.
• Essential for species survival and population maintenance.

Excretion is the process by which organisms eliminate metabolic waste products and excess substances that could be harmful if accumulated.

For example, humans excrete carbon dioxide via lungs and urea via urine. Plants excrete oxygen as a by-product of photosynthesis.

Efficient excretion maintains internal chemical balance and prevents toxicity.

• Removes wastes like carbon dioxide, urea, and excess salts.
• Maintains internal environment stability.
• Different organisms have specialized excretory systems.