ECOLOGY

Definition

The study of living things and their environment.

Why is the Sun the Ultimate Source of Energy?

Plants use the sun’s energy to make food during photosynthesis. Carbon dioxide is combined with water to produce glucose and oxygen.

Glucose is used to make other carbohydrates, lipids, proteins, and everything else the plant needs. These become the components of food. Food can be used for the term ‘energy’.

Energy Gains & Loss

How Plants Gain and Lose Energy

• Plants gain energy when they convert the light energy from the sun to chemical energy (food and other chemicals) during photosynthesis.

• It stores some of the energy by changing the glucose it makes into other chemicals.

• It uses up some of the food during respiration to release energy to grow and carry out other life processes.

• Some of the energy is lost as heat energy from the plant.

• ONLY SOME OF THE ENERGY TAKEN UP BY THE PLANT CAN BE PASSED ON TO A HERBIVORE.

How Animals Gain and Lose Energy

• Energy is gained as the organism feeds

• Some of the energy is stored as tissue as the animal grows

• Some of the energy is lost as faces and urine from the animal’s body

• Some of the stored energy is released during respiration by animals

• Some of the energy is lost as heat to the environment.

• As little as 10 percent of the energy at any trophic level is transferred to the next level; the rest is lost largely through metabolic processes as heat.

Bioaccumulation

Pesticides can spread through the environment in a food chain. Pesticides (fungicides, herbicides, and insecticides) are chemicals that are toxic to some organisms.

Pesticides can harm organisms in two ways:

• On contact

• The chemical enters the body of the organism

Symbiotic Relationships

Symbiosis

Any long-term interaction between two different biological organisms

Types of Symbiotic Relationships

Commensalism

A relationship between two different species in which one benefits and the other is not harmed.

Mutualism

Two organisms of different species live closely together, both benefit.

Parasitism

An organism (parasite) feeds on another organism (host), harming the host.

Food Webs & Chains

Food Chain vs Web

Food Chain

A linear sequence of organisms through which nutrients and energy pass as one organism eats another.

In a food chain, each organism occupies a different trophic level, defined by how many energy transfers separate it from the basic input of the chain.

Food Web

Consists of many interconnected food chains and are more realistic representation of consumption relationships in ecosystems.

Energy transfer between trophic levels is inefficient—with a typical efficiency of around 10%. This inefficiency limits the length of food chains.

Adaptations in Predators

• Speed

• Agility

• Weapons (Claws, Fangs)

• Ambush Tactics (camouflage)

Adaptations in Prey

• Excellent vision

• High speed

• Camouflage

• Defence

Producers & Consumers

Producer

Organisms that produce their own food using energy from sunlight (photosynthesis) or chemicals (chemosynthesis).

Consumer

Organisms that obtain energy by consuming other organisms or organic matter.

Primary Consumer

Herbivores that consume producers (plants or algae).

Secondary Consumer

Carnivores that eat primary consumers (herbivores).

Tertiary Consumer

Predators that feed on secondary consumers.

Trophic Levels

Positions in the food chain or web that indicate an organism's feeding status and energy source.

There are max four trophic levels because of the transfer of energy and nutrients in ecosystems. As energy is transferred between trophic levels, there is a loss of energy efficiency. By the time energy reaches the tertiary consumer level, there is often not enough energy left to support another level of consumers. Therefore, ecosystems typically sustain themselves with up to four trophic levels to efficiently transfer energy from producers to top predators while maintaining ecological balance.

Heterotrophs

Organisms that cannot produce their own food and rely on consuming other organisms for energy.

Autotrophs

Organisms that can produce their own food through photosynthesis or chemosynthesis.

Niche

The specific role or function of an organism within its ecosystem

OSMOSIS

Definition

The diffusion of water molecules from an area where they are in high concentration to an area where they are in low concentration through a partially permeable membrane.

Types of Solutions

Hypotonic Solution

A solution where the concentration of solutes outside the cell is lower than inside the cell. Animal cells become turgid and burst due to the absence of a cell wall, while plant cells swell and remain turgid due to their cell wall.

Hypertonic Solution

A solution where the concentration of solutes outside the cell is higher than inside the cell. The cell membrane pulls away from the cell wall in a process called plasmolysis. This causes water to move out of the cell, leading to shrinking or shrivelling of the cell (becoming flaccid).

Isotonic Solution

A solution where the concentration of solutes outside the cell equals that inside the cell. There is no net movement of water, so the cell maintains its shape and size.

Terms

Plasmolysis

The process in plant cells where the cell membrane pulls away from the cell wall due to water loss, typically occurs in a hypertonic environment.

Flaccid

A plant cell that lacks turgor pressure due to a loss of water. It becomes soft and limp

Turgid

A plant cell that is firm and swollen due to the uptake of water in a hypotonic environment, exerting pressure against the cell wall.

PHOTOSYNTHESIS

Definition

Process whereby green plants make their own food. They use simple inorganic substances ( CARBON DIOXIDE, WATER) to make glucose.

From the glucose, the plants can make other complex materials that it needs such as protein, carbohydrates, and fats.

Photosynthesis Equation

Carbon Dioxide + Water + Sunlight/Chlorophyll —> glucose + oxygen

6 CO2 + 6H2O + sunlight/chlorophyll —> C6H12O6 + 6O2

Importance of Chlorophyll

Chlorophyll is a complex green pigment. At the centre of the chlorophyll molecule is a single atom of magnesium and four atoms of nitrogen.

What Happens to Carbon Dioxide and Water During Photosynthesis

During photosynthesis, carbon dioxide (CO2) and water (H2O) are used by plants to produce glucose (C6H12O6) and oxygen (O2). The process involves the absorption of carbon dioxide from the atmosphere through tiny pores called stomata on the leaves. Water is absorbed from the soil by the roots and transported to the leaves through xylem vessels.

Products of Photosynthesis

The glucose produced during photosynthesis is used in several ways:

• It is broken down during respiration to release energy so the plant can carry out all the processes of life.

• It is converted to starch and stored in the leaf to be used in the night when the plant is not photosynthesising.

• It is converted to sucrose and transported to other parts of the plant. It can be converted to other carbohydrates, lipids and proteins and used for growth, or it can be converted to starch and stored, as in potatoes.

Limiting Factors that affect Photosynthesis

• Temperature

• Light intensity

• Carbon dioxide concentration

• Availability of water

Light Stages

Light Dependent Stage

This happens in the thylakoid of the chloroplast.

Chloroplasts are organelles seen in green plant cells. They contain the green pigment chlorophyll which traps the light energy from the sun.

This energy can produce two molecules: Adenosine Triphosphate (ATP) and Nicotinamide adenine dinucleotide phosphate (NADH). These molecules are high in energy which in the light-independent stage is used up in the synthesis of glucose.

The energy is used to split the water molecule H2O into hydrogen (h) and oxygen (o). The oxygen is a waste product and diffuses out of the leaf.

Light Independent Stage/Calvin Cycle

Through the use of enzymes, the hydrogen then combines with carbon dioxide (CO2) to make glucose (C6H12O6).

This stage of photosynthesis does not need light and can happen when it is dark.

Nutrition

The process by which organisms obtain and utilize nutrients for growth, maintenance, and energy production.

Autotrophic Nutrition

Making their own food from inorganic substances.

Heterotrophic Nutrition

Obtaining food by consuming other organisms or organic matter.

Types: Holozoic, Saprohytic, Parasitic

Simple Leaf Structure

Leaf Adaptations

• They are generally broad and flat with a large surface area to absorb a lot of light and carbon dioxide.

• They lie at 90 degrees to the sunlight and are spaced around the stem to catch as much light as possible.

• The leaves are thin to allow light and carbon dioxide to reach cells rapidly.

• Stomata are present in the lower epidermis to allow gases in and out easily.

• Air spaces in the lower leaf allow carbon dioxide to get to chloroplasts as quickly as possible.

• Chloroplasts are most numerous in cells in the palisade layer which is in the top part of the leaf, closest to the sunlight.

• Xylem vessels transport water to the leaf cells.

• Phloem sieve tubes carry away the food made to the rest of the plants.

• A waxy cuticle prevents water loss from both surfaces of the leaf and is transparent to let light through.

Xylem and Phloem

INTERNAL LEAF STRUCTURE

Parts of the Internal Leaf

Epidermis

The top and bottom of the leaf are responsible for protecting the inner layers of cells. The top epidermis secretes a waxy substance called cuticle which prevents water from evaporating from the leaf.

Stomata

Small holes/pores majority of which are found in the lower epidermis. Each stoma is surrounded by a pair of sausage-shaped guard cells. The guard cells are responsible for opening and closing the stoma. They contain chloroplast.

Mesophyll

‘Meso’ means middle, and ‘phyll’ means leaf.

These cells contain chloroplasts. The mesophyll layer located near the top of the leaf is arranged like a fence or palisade and they form the palisade layer. This is where most of the photosynthesis occurs in the leaf. They are closely packed together to maximize light absorption.

The cells behind them are rounder, and arranged quite loosely, with large air spaces between them. They form the spongy layer. The cells in this layer are loosely packed for efficient gas exchange. There is a thin layer of water which covers the cells. Gases dissolve in this water as they move into and out of the cells.

The mesophyll also contains veins. The two are the xylem ( a large thick- walled tube for carrying water & minerals) and phloem tubes (small with thin walls) carry away food that the leaf has made.

STARCH

REFER TO LABS

DIGESTIVE SYSTEM

Terms

Feeding/ingestion

Where food is taken into the body

Digestion

Where large, complex, insoluble food molecules are broken down into smaller, soluble molecules

Absorption

Where small, soluble food molecules are absorbed into the blood and into body cells

Assimilation

Where the food molecules are stored or used by the cells for respiration, growth

Egestion

Where undigested food is removed from the body

Diagram

EXAM CRITERIA

SECTION A: 30 MCQ

SECTION B: 2 STRUCTURED (30 MRKS)

TOPICS:

• Osmosis

• Ecology

• Digestive System

• Photosynthesis

• Starch (Photosynthesis)

• Internal Structure of the Leaf (Photosynthesis)