Anatomy and Physiology of

Plants and AnimalsLearning Goal

Describe systems for gas exchange, circulation, digestion, and excretion in plants, animals, and humans.

Plants

• Gas Exchange – Openings on the

underside of leaves, called stomata, allow plants to take in carbon dioxide and give off oxygen during photosynthesis.

– Cells called guard cells surround the stomata and cause them to open and close in response to water pressure within the guard cells.

• Circulation • Water and food are

transported throughout plants in tube-like vascular tissue called xylem and phloem.

• Water moves through xylem from the roots.

Mechanical Properties of Water

• Transpiration – Evaporation of water out of plants– Greater than water used in growth and metabolism

• Cohesion-tension mechanism of water transport– Evaporation from mesophyll walls– Replacment by cohesion (H-bonded) water in xylem– Tension, negative pressure gradient, maintained by

narrow xylem walls, wilting is excess tension

• Sugars made by the plant for food are moved from the leaves where photosynthesis takes place into other parts of the plant in the phloem.

Movement of Organic Substances Through Phloem

• Source: Any region of plant where organic substance is loaded into phloem– Companion and transfer cells, use free

energy• Sink: Any region of plant where organic

substance is unloaded from phloem• Pressure flow mechanism moves substance by

bulk flow under pressure from sources to sinks– Based on water potential gradients

Digestion

Plants don’t have to digest their food the way animals do because they take in very small nutrients and make their own sugar molecules.

Excretion

The stomata act as openings through which by-products of photosynthesis and cellular respiration exit (CO2 O2, and H2O)

Invertebrates

– Gas Exchange – Most aquatic

invertebrates exchange oxygen and carbon dioxide through gills. They are feathery structures that expose a large surface area to the water. Examples: mollusks, arthropods.

• Terrestrial invertebrates have respiratory surfaces covered with water or mucus. They range from book lungs in spiders

to spiracles (openings) that open into tracheal tubes in insects.

• Circulation • Open circulatory

system – blood contained in vessels and sinuses (large spaces) pumped by one or more heart-like organs. Examples: arthropods and most mollusks

• Closed circulatory system – a heart-like organ forces blood through vessels that extend throughout the body. Examples: annelids and some mollusks

Digestion

Intracellular digestion

Small particles of food enter cells, and are broken down, then nutrients are passed to other cells.

Examples: sponges, jellyfish

Extracellular digestion Food is broken down outside of cells in a digestive cavity or tract then absorbed by cells. Examples: mollusks, annelids, arthropods

Excretion:

Aquatic Invertebrates Ammonia (a toxic by-product of protein break down) moves out of cells directly into surrounding water.

Terrestrial Invertebrates Tube-like structures called nephridia turn ammonia into less toxic substances like urea and uric acid, then release it into the environment.

Vertebrates

– Gas Exchange – Gills in aquatic

vertebrates like fish and amphibian larvae (tadpoles)

– Lungs in terrestrial vertebrates like mature amphibians, reptiles, birds, and mammals.

– Both gills and lungs consist of moist surfaces containing many tiny blood vessels through which oxygen and carbon dioxide move.

• Circulation • Fish – single loop

circulatory system with a two chambered heart.

• Amphibians – double loop system with one loop carrying blood between the heart and lungs and the other loop carrying blood between heart and rest of body. Heart has three chambers.

• Most reptiles have a double loop system with a three chambered heart, but the heart is partitioned so that there is less mixing of oxygen-poor and oxygen-rich blood than in amphibians.

• Birds, mammals, and crocodilians have a four-chambered completely divided heart in a double loop system.

Digestion

All vertebrates have extracellular digestion with digestive organs suited for different feeding habits.

Carnivores have short digestive tracts, while herbivores have longer digestive tracts.

Excretion

Most vertebrates rely on kidneys to get rid of nitrogenous waste.

As proteins are broken down, ammonia forms but is converted to less toxic urea or uric acid, then eliminated by the kidneys.Kidneys are also important in regulating water and other substances in body fluids.