DIFFERENCES BETWEEN PLANTS AND ANIMALS
|Green plants carry out photosynthesis||Animals cannot carry out photosynthesis; they depend on plants for their food.
|Plants do not move from one place to another and do not have organs of movement.||Animals move from one place to another and have organs of movement. They exhibit locomotion.
|Growth is indefinite (continues throughout life) and apical.||Growth is definite and occurs uniformly in every part of the body. It stops when they become adults.
|Plants do not have specialized organs for excretion, respiration and coordination.||Animals have specific organs for excretion, respiration and coordination.
|Plants are slow in response to stimuli||Animals are fast in their response to stimuli
|Excess carbohydrates are stored as starch
|Excess carbohydrates are stored in form of glycogen|
|They have many branches||They do not have any branches|
Some organisms exist which possess characteristics of both plants and animals an example is Euglena Viridis. Euglena Viridis is a microscopic unicellular organism, which lives in water.
The characteristics of Euglena which make it an animal are;
- Possession of flagellum used for movement.
- Possession of gullet for passage of food and which acts as a reservoir.
- The presence of an eyespot enables it responds to light.
- Possession of contractile vacuole used for excretion.
- Possession of pellicle which makes its body flexible.
- It can feed on other organisms (holozoic nutrition) in the absence of sunlight.
The plant characteristics of Euglena are;
- The possession of chloroplast enables it to carry out photosynthesis.
- Possession of pyrenoid where starch is stored
- It can produce its own food (holophytic or autotrophic nutrition).
LEVELS OF ORGANISATION OF LIFE
- The bodies of living things are highly organized.
- This organization occurs in levels, with the simplest structure occurring at the lowest levels (single cells) which interact to build up more complex structures (multicellular organisms).
- The basic levels of organization of life in organisms are; cells, tissues, organs, and systems.
- This is the smallest unit of a living organism. It is the first and simplest level of organization of life. Plants and animals are made up of cells.
- One celled organism is called a unicellular organism. They include Amoeba, Plasmodium, Euglena, Paramecium, etc. Organisms made up of many cells are called multicellular organisms e.g man, mango, trees, etc.
- The single-celled organism can carry out all life processes on its own.
- This is a group of similar cells that come together to perform a particular function.
- A tissue consists of two or more different types of cells aggregating together to perform a specific function e.g. the mesophyll layer in leaves, xylem tissue in stems, muscles, blood (a liquid tissue), etc.
- Organisms that exist at the tissue level include the hydra, jellyfish, sponge, etc.
- Is a group of similar tissues which come together to perform a specific function.
- Examples in plants are flowers, roots, leaves, seeds, a rhizome, a corm, an onion bulb, a tuber, etc.
- Examples in animals are the skin, stomach, heart, brain, liver, eyes, ears, kidney, etc.
- This is a group of functionally related organs that work together to perform specific functions. Examples in plants include the shoot system and root system.
- Examples in animals include the digestive, nervous, excretory and circulatory systems.
- Examples in plants are the transport system, shoot and root system.
Complex multicellular organisms
- The climax of organization in higher living things is the aggregation of systems to form an organism.
- Complex multicellular organisms are composed of several organ systems which work harmoniously for the benefit of the organism.
- All animals from Platyhelminthes to Mammals and all vascular plants are organized on this level.
The complexity of Organization In Higher Animals
As organisms acquire more layers of cells, they become complex in structure, thus there is an increase in complexity from unicellular to multicellular organisms.
Advantages of Complexity
- It leads to cellular differentiation, thus groups of similar cells are differentiated to form tissues which carry out similar functions
- It leads to internal structural specialization in which the tissues become specialized to carry out specific functions.
- There is mutual interdependence between component cells i.e division of labour among the cells.
- Complexity makes higher organisms to be more efficient in carrying out life processes.
- Complexity leads to increase in size of organisms.
- It makes it possible for organisms to become more resistant to adverse condition within the environment.
Disadvantages of Complexity
- The cells lose their independence and become increasingly dependent on one another’s activities.
- Difficulties in acquisition of materials (such as oxygen and food materials) and removal of waste products by the millions of cells making up a multicellular organism
- Slower rate of diffusion of oxygen or respiratory gas to individual cells.
- Slower rate of expulsion of waste products from cells.
- Decrease in ability to regenerate
- Difficulties in reproduction.