From Chapters 39 and 51.

Main Points:

  1. 95% of living tissue is C, H, O, N, P and S; 26 elements in total are found in living tissues.
  2. Elements other than C typically enter the life system through plant roots.
  3. Plants absorb water into their roots and lose it from their leaves.
  4. Nutrients move up the stem of plants while carbohydrates move down the stem.
  5. Plant growth is significantly influenced by the nature of the soil.
  6. Plants require large amounts of some nutrients but only trace amounts of others.
  7. Some plants obtain nutrients by capturing and digesting insects.
  8. Animals use a digestive system to facilitate the assimilation of nutrients.
  9. Villi and microvilli absorb glucose, amino acids and fatty acids into the blood .
  10. All animals require food energy and essential nutrients

I. The elemental Composition of Life

Living things are composed of much more more than Carbon, Oxygen and Hydrogen (the elements we have followed so far through photosynthesis and respiration). What are the other elements and where do they come from?

The Chemistry of Life Reflects the Chemistry of the Early Earth

  1. Life reflects the overall elemental abundance of the Earth, and the specifically the elements found at the surface.
  2. Striking correlation between elemental abundances in the biota and the SOLUBILITY of the elements in ocean water
  3. Three constraints on the elements that compose life

II. Water and nutrient movement through plants.

Elements other than C typically enter the life system through plant roots

Minerals and water in the ground must be absorbed by the roots and transported up to the leaves and other parts of plants.

Figure 35.1 from your textbook

Most nutrients are transported in solution, within the water conducting tissues of plants, similar to the way nutrients circulate in the blood stream animals. Unlike animals, plants to not have hearts to pump the conducting solution with, so how does water move through a plants?

The evaporation of water from the leaves of plants pulls water through to plant, and the water lost is then replaced from the soil surrounding the roots.

Figure 35.4 from your textbook

The loss of water from the leaf surface, called transpiration, literally sucks water up the stem from the roots. Water rises up the stem because the water potential (total potential energy of the water in a plant) in the roots is greater than that in the leaves. That is to say water moves along a concentration gradient from wet soils that have a relatively high water potential (but variable), to roots, stems, leaves and the atmosphere each at a relatively lower water potential

The Absorption of Water by Roots

Primarily through root hairs

Ions may follow the cell walls and the spaces between them

Ions can also move directly through the plasma membranes and the protoplasm of adjacent cells

Figure 35.5 from your textbook

Once in the root, water and minerals enter the Vascular cylinder - the conducting tissue of the plant, and transpiration from the leaves moves the water and minerals through the plant.

Figure 35.6 from your textbook

Transpiration of Water from Leaves

More than 90% of the water that is taken in by the roots of the plant is ultimately lost to the atmosphere

Stomata regulate water loss and carbon gain

Figure 35.8 from your textbook

Nutrient Movement

Ion Transport through the Xylem

Carbohydrate Translocation is through the Phloem

Figure 35.10 from your textbook

III. Plant Growth is significantly influenced by the nature of the soil

Soil is the highly weathered outer layer of the earth's crust

Figure 36.2 from your textbook

Topsoil is a mixture of mineral particles, living organisms and humus (partly decayed organic material) where most of the roots live, and therefore where most of the minerals found in living things come from.

Soil particles vary in size from 2000 micrometers less than 2 micrometers in diameter.

Roughly half the soil volume is occupied by spaces or pores which may be filled with air or water.

Figure 36.3 from your textbook

Water in soil

Can be tightly bound to soil particles that bear electrostatic charges or that are able to form hydrogen bonds.

The higher the surface area, the more tightly the water will adhere to the soil.

Water can become so tightly held that it is unavailable to the plants.

Field Capacity is the amount of water held in a given soil after the excess has been removed by gravity.


Decomposition and nitrogen fixation continually add nutrients to the soil.

Plants remove available nutrients from the soil around the roots more quickly than it can be replaced.

Soil Fertility, is the ability of the soil to supply the plants with the nutrients needed for growth.

Many nutrients are returned to soils after plant death and decay.

Crop harvesting or otherwise removing the plant material limits the return of minerals to the soils.

Crop rotation can increase the soil fertility.

N fixers, non-nitrogen fixers.

Plowing under plant material helps maintain soil fertility.

Figure 36.5 from your textbook


Soil nutrition can be amended by the addition of fertilizers.

The most important mineral nutrients added to soils are N, P and K.

Micronutrient deficiencies can also exist.

Figure 36.6 from your textbook

Plant Nutrients

Macronutrients - needed in relatively large amounts (approximately 1 % of the dry plant mass).

9 elements - C, H, O, N, K, Ca, P, Mg, S

Micronutrients - needed in relatively small amounts (1 to several hundred ppm).

7 elements - Fe, Cl, Cu, Mn, Zn, Mo Bo

Table 36.1 from your textbook

IV. Carnivorous Plants

Some plants are able to obtain nitrogen directly from other organisms, just as animals do.

Figure 36.8 from your textbook

V. Animals use a digestive system to facilitate the assimilation of nutrients

Heterotrophs must consume organic molecules other organisms have already produced.

These organic molecules must be digested into smaller molecules in order to be absorbed into the animals body.

Most animals digest their food extracellularly. A digestive tract with a one-way transport of food and specialization regions for different functions, allows food to be ingested, physically fragmented, chemically digested and absorbed.

Figure 48.2 and 48.3 from your text

Nutrients and organic molecules are absorbed in the digestive tract, which therefore has been modified to have a very large surface area. The surface area of a human small intestine is 300 square meters!

Digestive enzymes are embedded within the epithelial cells and the active site is exposed to the digestive tract.

Figure 48.13 from your textbook

The terminal steps in digestion are catalyzed by brush border enzymes contained with in the plasma membrane of the microvilli of the small intestine.

Figure 48.15 from your textbook

Monosaccharides and amino acids are transported into blood capillaries while fatty acids and monoglycerides within the intestinal lumen are absorbed and converted into triglycerides and eventually enter the lymphatic capillaries.

Figure 48.16 from your textbook

The ingestion of food serves two primary functions

  1. source of energy
  2. raw materials

Many animals are unable to synthesize specific substances that are critical in their metabolism. Substances that must be ingested and are critical to health of the animals are referred to as Essential Nutrients.

Vitamins are organic substances required in trace amounts

Amino acids - many vertebrates can not produce all 20 amino acids used to make proteins.

Certain unsaturated fatty acids can not be synthesized in vertebrates.

Essential minerals are also supplied in food.

Ca, P, I,Co, Zn, Mo, Mn, Se

Table 48.3 from your textbook

Useful Links

Plant Nutrition

Lecture by Professor Kevin Griffin.

Updated April 20, 2005
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