a. Plants and animals are primarily distinguished by their modes of nutrition, and this distinction dictates their very different forms (Table 32.1).

b. Plants are sessile phototrophs, growing in one place and unable to move around.

c. A typical plant (Figure 32.1) has a central vertical column divided into a root system, a shoot system, and a vascular system.

d. Plant roots and shoots are radiated largely symmetrically to all sides (Figure 32.2).

e. Animals do not photosynthesize, and thus are chemotrophs that are also holotrophic: they engulf pieces of food and digest them internally (Figure 32.3).

f. Animals generally are motile and need to move in order to obtain food or flee from predators.

g. Cephalization, the development of a head end with specialized sensory structures (Figure 32.4), was a major step in the evolution of the animal body plan.

h. Terms like anterior, cephalic, posterior, and caudal, are all derived to reference structures with regard to the head end of an animal.

i. Animals have digestive tracts that process food and absorb nutrients into their bodies.

j. Most animals have bilateral symmetry (Figure 32.5), meaning their bodies can be divided into right and left mirror images by a plane through their middle, and also meaning they have upper (dorsal) and lower (ventral) sides.

k. Animals thus locomote through sets of right and left muscles or other structures arranged symmetrically (Figure 32.6).

a. Animals that have a sessile existence, as do those which live on substrates in the ocean, exhibit radial symmetry, and have all their parts arranged around a central axis (Figure 32.7).

b. These animals tend to also have feeding structures (e.g. tentacles) that take advantage of the fact that their food moves past them as they stay in one place.

a. A tissue, such as the photosynthetic tissues in a leaf, a nervous tissue, or a muscle tissue, is a mass of similar cells that are specialized for some function.

b. Organs, such as a leaf, a root, a heart, or a lung, are made of several kinds of tissues working together for a specific function.

c. Three general types of tissues exist in both plants and animals.

d. Surface tissues form a boundary, protect, and transport materials into or out of the organism.

e. Connective or mechanical tissues provide support for both plants and animals and also a framework for movement for animals.

f. Bulk tissues include relatively undifferentiated cells packed into the matrix of supporting cells.

a. Organs generally share several features (Figure 32.13):

b. An organ system in an animal is a collection of organs, such as the brain, nerves, and sense organs in the nervous system.

a. Both plants and animals can be either unitary or modular (Figure 32.14).

b. A unitary organism is a distinct individual with features that do not change over its lifetime.

c. Animals are most typically unitary (except sponges) and plants are most typically modular.

d. Grasses and strawberry plants, for example, grow by sending out new modules with roots and shoots (Figure 32.15).

e. Figure 32.16 shows examples of modular organization in both plants and animals.

f. Determinate growth means growing to a definite size but no further, and is a characteristic of unitary organisms.

g. Indeterminate growth means adding new modules without limit, and characterizes most modular organisms.

a. Photosynthesis involves the conversion of carbon dioxide and water into oxygen and glucose.

b. Respiration converts glucose and oxygen into carbon dioxide and water.

c. Water is obviously necessary for plants to photosynthesize, but they also respire for energy.

d. Water is a requirement for plants and animals, and terrestrial organisms are constantly challenged to get enough water.

e. Plants synthesize their own amino acids and other nitrogenous compounds, but animals generally end up excreting excess nitrogen, thus plants and animals have different nitrogen requirements.

a. Both plant and animal cells exchange gases with their surroundings.

b. Small organisms and plants tend to accomplish this exchange by diffusion alone; large animals have a circulatory system.

c. Arthropods such as insects and spiders both have a system of tracheae (singular trachea), which are fine branching tubules that supply gases to their cells (Figure 32.17).

d. An extensive intracellular gas space system of air-filled channels exists in vascular plants (Figure 32.17), and allows gas exchange during respiration and photosynthesis.

e. Stomata are openings in plant leaves (Figure 32.17) that allow gases to leave.

a. Cells are bathed in an extracellular fluid (Figure 32.18) that has a different composition from the intracellular fluid (the cytosol).

b. In animals, the extracellular fluid is interstitial fluid, and materials move into and out of cells via this fluid, the composition of which is maintained by the animal's regulatory activities.

c. In vascular plants, large blocks of cells share a common intracellular space, and the cytoplasm of these interconnected cells comprises the symplast of the plant (Figure 32.19).

d. The extracellular space of plants is called the apoplast, and consists of the intercellular space and the fibrous walls.

a. Each plant and animal habitat presents its own water balance problems (Figure 32.20).

b. Water may be scarce either because it does not exist or because it is mixed with salts.

c. Homeohydric organisms, such as humans, maintain hydration within narrow limits.

d. Poikilohydric organisms have water contents that vary with their environments, and these organisms can withstand dessication to various degrees.

e. Some organisms can enter a cryptobiotic state, in which they are severely dehydrated and carry out little metabolism, and after which they can return to a normal life.

f. The cytoplasm of all cells is approximately isotonic with sea water, indicating that early evolution occurred in a sea water environment.

g. Cytoplasm is therefore hypertonic to fresh water, and protistans evolved two ways to resist an influx of water into their cells (Figure 32.21).

h. Algae have strong walls that allow high turgor pressure to build up inside the cell, producing a turgid cell.

i. Freshwater protozoa evolved contractile vacuoles, which accumulate and then flush out excess water.

j. Many marine animals do not regulate the osmolarity of their extracellular fluid; they are in osmotic equilibrium with their surroundings and are called osmoconformers.

k. Osmoregulators are animals that can regulate their extracellular fluids, and they can live in changeable environments.

l. Terrestrial plants and animals face continual water loss through transpiration, the loss of water vapor.

m. Plants and animals are also challenged by extremely salty conditions, and the roots of most plants have evolved mechanisms to exclude salt from their tissues.

n. Marine animals, reptiles, and birds, evolved glands that excrete concentrated salt solutions.

o. Water regulation is governed by an important principle (Figure 32.22): Water cannot be moved by itself, because cells have no water pumps; instead, cells transport ions.

a. Algae and mosses have no vascular system, and exchange water and nutrients directly with their surroundings.

b. Most terrestrial plants have an extensive shoot system, a root system, and a vascular system that communicates between the producing and consuming portions.

c. The plant vascular system is made of two kinds of tissues (Figure 32.23): xylem to carry water and minerals upward from the roots, and phloem to carry sugars and other organic products from the leaves to places where they are stored or used.

d. The plant vascular system has allowed adaptations to terrestrial environments.

e. Small aquatic animals also exchange water and minerals directly with their environment, but larger or terrestrial animals have a vascular system.

f. Commonly, a contractile heart (Figure 32.23) pumps fluids that are usually carried inside a set of tubes; these form a cardiovascular or circulatory system in animals.

g. Vertebrates have a closed circulatory system, in which the circulating fluid is confined to vessels.

h. The majority of animal species – arthropods and molluscs – have an open circulatory system with an extracellular fluid that bathes tissues and is circulated in only a few confined vessels.

a. Sexual reproduction must have begun in aquatic environments and has evolved into a system that typically involves free-swimming sperm that must find eggs; the eggs are typically released or held inside a receptacle (Figure 32.24).

b. The earliest terrestrial plants also have motile sperm, but plants eventually evolved pollen and seeds, which allow reproduction in a variety of environments (Chapter 33).

c. The most dominant animals have generally replaced external fertilization with internal fertilization.

d. The reproductive success of reptiles and birds was linked to the development of eggs with a tough protective shell and a self-contained food supply.

a. Small organisms live faster and reproduce faster than large ones (Figure 32.25).

b. Figure 32.25 shows an allometric relationship, where y = kx2.

c. Biological forms are shaped by elementary physical principles, one of the most important of which is that the surface to volume ratio of a structure decreases as the structure becomes larger.

d. This principle constrains the form of structures, including the small sizes of cells (Section 6.3), wherever the activity within a volume is limited by the transport of materials through the surface.

e. The rate at which a substance diffuses between two points is described by Fick's Law: Q = DA(C1 - C2)/L.

f. Here, Q is the rate of diffusion, and D is the coefficient of diffusion, A is the cross-sectional area through which the substance is diffusing, C1 and C2 are the concentrations of the substance at the two points, and L is the distance between them.

g. The coefficient of diffusion, D, is a constant for each substance at a given temperature and medium, increases with the volatility of the substance, and is higher in air than in water.

h. The concentration gradient is represented by (C1 - C1)/L in this equation.

i. Fick's Law provides a foundation for analyzing biological structures that involve transport of materials.

j. Rapid transport requires a large surface area (A) and the smallest possible distance (L), implying a reduced volume for diffusion.

k. Figure 32.26 illustrates this concept with regard to a vascular system; a single large tube can handle a large volume, but many small vessels carry the same volume and have collectively a much larger surface, for an increased surface to volume ratio and improved diffusion.

l. Thus, the branching structure of a typical cardiovascular system provides vessels with high surface to volume ratios; plant roots achieve this with root hairs (Figure 32.27).

m. Plants living in arid conditions achieve low surface to volume ratios with thick, knobby leaves, and thus minimize water loss through evaporation.

a. An object's strength increases with its cross-sectional area, a fact that dictates the sizes of many biological structures.

b. As an object increases in size, the cross-sectional area of its supports must increase with the square of a dimension and its volume, hence its mass increases with the cube of a dimension.

c. A mammal's skeletal supports (Figure 32.28) involve mass-bearing bones of certain cross-sections; the heavier animals have relatively shorter and thicker legs.

d. The same considerations constrain an animal's movements, as its mass on which it pulls increases with the cube of a dimension.

e. The size and forms of plants are determined in much the same way; herbaceous plants remain small and fragile, but the limbs of a tree must grow thick to support branches, foliage, and fruit.

a. Every organism is adapted to living within a certain temperature range.

b. Aquatic organisms are generally not subjected to severe changes in temperature, since water changes temperature slowly.

c. Terrestrial organisms live in environments with extreme shifts in temperature, both on a daily and a yearly basis.

d. Plants and most animals are poikilothermic ("cold-blooded") and they must obtain most of their heat from the outside, meaning they are also ectothermic.

e. Ectotherms regulate their temperatures largely by their behavior, as when reptiles sun themselves, plants open or close their leaves, or insects open or close their wings (Figure 32.29).

f. Birds and mammals are endothermic, meaning they use metabolic heat to maintain a fairly constant body temperature, as they are also homeothermic ("warm-blooded").

g. Homeotherms metabolize 3 to 10 times faster than poikilotherms of the same size, and they have extra insulation to conserve heat.

h. Homeotherms also have internal thermostats that monitor their blood temperature and initiate mechanisms, such as panting or sweating, to keep it constant.

i. Some organisms can reduce their metabolic activities to very low rates without harm.

j. Homeothermic animals have a basal metabolic rate (BMR), the rate of metabolism that just keeps the animal alive.

k. The standard metabolic rate (SMR) is an equivalent measurement of metabolism for a poikilotherm, and varies with body temperature.

l. Figure 32.30 shows that an animal's metabolic rate (m) is related to its weight (w) in a simple way: m = kw0.75, where k is 0.018 for unicellular organisms, 0.14 for poikilotherms, and 4.1 for homeotherms.

m. A comparison of metabolic rates per gram of body weight (Figure 32.31) shows that small animals metabolize much faster for their size than large ones do.

n. A small homeotherm produces heat in a small volume but loses it through a relatively large surface (Figure 32.32); thus small animals have to work hard to stay warm and they have high BMR values.

o. This relationship sets the lower limit to the size of an endothermic animal.

p. Other features of endothermic animals are determined by surface to volume considerations.