BIO 7:  Lecture 20-21 Preview

Large organisms need support structures to give them shape and keep cells from smashing other cells with their weight. 

• Support structures may be made of cell wall carbohydrates, water, organic molecules, and/or minerals.
• There is a trade-off between the strength of the support structure and its weight.
• There is a trade-off between the stiffness of the support structure and its flexibility.

Different support materials have advantages and disadvantages.

Some common structures considered to be skeletons include

• shells made of minerals like calcium and phosphorous cover clams, oysters, and other mollusks
• exoskeletons made of the carbohydrate chitin cover insects, crustaceans, and other arthropods
• endoskeletons made of a combination of cells, minerals, and organic material like collagen are found in vertebrates

 Energy needed to carry around different skeletons varies.

The vertebrate skeleton uses a number of compromises.

• A mixture of cells with minerals and organic material allows bones to grow and repair themselves.
• A mixture of organic and mineral material allows strength, lightness, and some flexibility.
• Joints provide more flexibility by letting bones move over limited ranges.

Skeletons also help animals move by acting as rigid levers pulled by muscles.

Living things are made of molecules, which function best under specific conditions; temperature and water concentration are especially important conditions.  Homeostasis is the process of maintaining fairly constant internal conditions.

• Very high temperatures "cook" proteins; very low temperatures slow down molecules and change water to ice.
• Lack of liquid water prevents other ions and molecules from moving around freely
• Living things have structures and activities that help them function under fairly constant conditions.

For homeostasis gain = loss

Water is gained and lost differently in water and on land.

Larger animals have internal mechanisms to maintain water content.  Humans have an excretory (or urinary) system.

Heat is gained and lost in different ways in water and on land.

Some mechanisms for gaining and losing heat.

Endotherms (mainly birds and mammals) keep their body temperature fairly constant;  ectotherms' body temperatures vary with the outside temperature.

Energy is required to maintain a constant body temperature.  What is the endotherm's advantage?

The integumentary system helps to regulate temperature and prevent water loss.