soil

Question 1

define soil

Answer 1

extreme outer part of earths crust

Question 2

describe inorganic rock particles (7)

Answer 2

formed from rocks weathering
classified by size
clay less 0.002 mm
silt 0.002 - 0.02 mm
sand 0.02-2.0 mm
gravel more than 2.0
form soil skeleton
provides support and firm anchorage for plant roots
provide surface for attachment of soil microorganisms
provide shelter for soil animals

Question 3

water (6)

Answer 3

obtained from waterfall
held in thin film around surface of soil particles by capillarity and chemical forces
essential for photosynthesis in plants
smaller soil particles large surface area and more water held because air spaces larger - more leaching of nutrients
dissolves mineral salts for absorption by plant roots
prevents desiccation of organisms without a waterproof body covering

Question 4

air (5)

Answer 4

occupies spaces in between soil particles
larger soil particles larger air spaces between them because smaller particles more closely packed leaving fewer spaces for air
easily displaced by water
o2 in air essential for respiration of planet roots and s organisms and necessary for aerobic humus
n2 for nitrogen fixing bacteria to form nitrates

Question 5

mineral salts (3)

Answer 5

formed from humans and by dissolving from surrounding rock
present as mineral ions dissolved in soil water
essential for healthy plant growth

Question 6

humus (8)

Answer 6

formed from dead and decaying organic matter
dark brown sticky material
adds mineral salts
binds soil particles together in small groups called soil crumbs which makes soil have good drainage
absorbs and retains water and mineral salts
helps insulate soil against extremes of heat and cold
forms coating around soil particles mainly in topsoil
helps prevent erosion by binding soil particles together

Question 7

soil organisms

Answer 7

bacteria - decompose organic matter forming humus and important in nutrient cycles
worms and burrowing animals - improve aeration and drainage by burrowing, improve fertility by adding humus, pull leaf litter- burrows excrete waste decompose when dead bring leached minerals into supper layers grind coarse soil particles
plant roots - bind soil particles preventing erosion